Photovoltaic element

ABSTRACT

A photovoltaic element ( 110 ) is proposed for conversion of electromagnetic radiation to electrical energy, more particularly a dye solar cell ( 112 ). The photovoltaic element ( 110 ) has at least one first electrode ( 116 ), at least one n-semiconductive metal oxide ( 120 ), at least one electromagnetic radiation-absorbing dye ( 122 ), at least one solid organic p-semiconductor ( 126 ) and at least one second electrode ( 132 ). The p-semiconductor ( 126 ) comprises silver in oxidized form.

FIELD OF THE INVENTION

The invention relates to a photovoltaic element, to a process forproduction of a solid organic p-semiconductor for use in an organiccomponent, and to a process for production of a photovoltaic element.Such photovoltaic elements and processes are used to convertelectromagnetic radiation, especially sunlight, to electrical energy.More particularly, the invention can be applied to dye solar cells.

STATE OF THE ART

The direct conversion of solar energy to electrical energy in solarcells is based generally on what is called the “internal photo effect”of a semiconductor material, i.e. the production of electron-hole pairsby absorption of photons and the separation of the negative and positivecharge carriers at a p-n junction or a Schottky contact. In this way, aphotovoltage is generated, which, in an external circuit, can cause aphotocurrent through which the solar cell releases its power. Thesemiconductor can generally only absorb those photons which have anenergy greater than the bandgap thereof. The size of the semiconductorbandgap thus generally determines the proportion of sunlight which canbe converted to electrical energy.

Solar cells based on crystalline silicon were produced as early as the1950s. The technology at that time was supported by use in spacesatellites. Even though silicon-based solar cells now dominate themarket on Earth, this technology still remains costly. Attempts aretherefore being made to develop new approaches which are less expensive.Some of these approaches will be outlined hereinafter, which constitutethe basis of the present invention.

An important approach to the development of new solar cells is that oforganic solar cells, i.e. solar cells which comprise at least oneorganic semiconductor material, or solar cells which, instead of solidinorganic semiconductors, comprise other materials, especially organicdyes or even liquid electrolytes and semiconductors. A special caseamong the innovative solar cells is that of dye solar cells. The dyesolar cell (DSC) is one of the most efficient alternative solar celltechnologies to date. In a liquid variant of this technology,efficiencies of up to 11% are currently being achieved (see, forexample, Grätzel M. et al., J. Photochem. Photobio. C, 2003, 4, 145;Chiba et al., Japanese Journal of Appl. Phys., 2006, 45, L638-L640).

Dye solar cells, of which there are now several variants, generally havetwo electrodes, at least one of which is transparent. According to theirfunction, the two electrodes are referred to as “working electrode”(also “anode”, generation of electrons) and “counterelectrode” (also“cathode”). On the working electrode or in the vicinity thereof, ann-conductive metal oxide has generally been applied, especially as aporous, for example nanoporous, layer, for example a nanoporous titaniumdioxide (TiO₂) layer of thickness approx. 10-20 μm. Between the layer ofthe n-conductive metal oxide and the working electrode, it isadditionally possible for at least one blocking layer to be provided,for example an impervious layer of a metal oxide, for example TiO₂. Then-conductive metal oxide generally has an added light-sensitive dye. Forexample, on the surface of the n-conductive metal oxide, a monolayer ofa light-sensitive dye (for example a ruthenium complex) may be adsorbed,which can be converted to an excited state by absorption of light. At oron the counterelectrode, it is frequently a catalytic layer of a few μmin thickness, for example platinum. The area between the two electrodesin the conventional dye solar cell is generally filled with a redoxelectrolyte, for example a solution of iodine (I₂) and/or potassiumiodide (KI).

The function of the dye solar cell is based on absorption of light bythe dye. From the excited dye, electrons are transferred to then-semiconductive metal oxide semiconductor and migrate thereon to theanode, whereas the electrolyte ensures charge balance via the cathode.The n-semiconductive metal oxide, the dye and the electrolyte are thusthe essential constituents of the dye solar cell.

However, the dye solar cell produced with liquid electrolyte in manycases suffers from nonoptimal sealing, which can lead to stabilityproblems. The liquid redox electrolyte can especially be replaced by asolid p-semiconductor. Such solid dye solar cells are also referred toas sDSCs (solid DSCs). The efficiency of the solid variant of the dyesolar cell is currently approx. 4.6-4.7% (Snaith, H., Angew. Chem. Int.Ed., 2005, 44, 6413-6417).

Various inorganic p-semiconductors such as CuI, CuBr.3(S(C₄H₉)₂) orCuSCN have been used to date in dye solar cells in place of the redoxelectrolyte. It is also possible, for example, to apply findings fromphotosynthesis. In nature too, it is the Cu(I) enzyme plastocyaninewhich, in photosystem I, reduces the oxidized chlorophyll dimer again.Such p-semiconductors can be processed by means of at least threedifferent methods, namely: from a solution, by electrodeposition or bylaser deposition.

Organic polymers have also already been used as solid p-semiconductors.Examples thereof include polypyrrole, poly(3,4-ethylenedioxythiophene),carbazole-based polymers, polyaniline, poly(4-undecyl-2,2′-bithiophene),poly(3-octylthiophene), poly(triphenyldiamine) andpoly(N-vinylcarbazole). In the case of poly(N-vinylcarbazole), theefficiencies extend up to 2%. PEDOT (poly(3,4-ethylenedioxythiophene)polymerized in situ also showed an efficiency of 0.53%. The polymersdescribed here are typically not used in pure form, but rather withadditives.

Inorganic-organic mixed systems have also already been used in place ofthe redox electrolyte in dye solar cells. For example, CuI was usedtogether with PEDOT:PSS as a hole conductor in sDSC (Zhang J. Photochem:Photobio., 2007, 189, 329).

It is also possible to use low molecular weight organicp-semiconductors, i.e. nonpolymerized, for example monomeric or elseoligomeric, organic p-semiconductors. The first use of a low molecularweight p-semiconductor in solid dye solar cells replaced the liquidelectrolyte with a vapor-deposited layer of triphenylamine (TPD). Theuse of the organic compound2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spiro-bifluorene(spiro-MeOTAD) in dye solar cells was reported in 1998. It can beintroduced from a solution and has a relatively high glass transitiontemperature, which prevents unwanted crystallization and poor contact tothe dye. The methoxy groups adjust the oxidation potential ofspiro-MeOTAD such that the Ru complex can be regenerated efficiently. Inthe case of use of spiro-MeOTAD alone as a p-semiconductor, a maximumIPCE (incident photon to current conversion efficiency, external photonconversion efficiency) of 5% was found. When N(PhBr)₃SbCl₆ as a dopant,and Li[CF₃SO₂)₂N] were also used, the IPCE rose to 33%, and theefficiency was 0.74%. The use of tert-butylpyridine as a solidp-semiconductor increased the efficiency to 2.56%, with an open-circuitvoltage (V_(oc)) of approx. 910 mV and a short-circuit current I_(sc) ofapprox. 5 mA at an active area of approx. 1.07 cm² (see Krüger et al.,Appl. Phys. Lett., 2001, 79, 2085). Dyes which achieved better coverageof the TiO₂ layer and which have good wetting on spiro-MeOTAD showefficiencies of more than 4%. Even better efficiencies (approx. 4.6%)were reported when the ruthenium complex was equipped with oxyethyleneside chains.

L. Schmidt-Mende et al., Adv. Mater. 17, p. 813-815 (2005) proposed anindoline dye for dye solar cells with spirobifluorenes as the amorphousorganic p-conductor. This organic dye, which has an extinctioncoefficient four times higher than a ruthenium complex, exhibits a highefficiency (4.1% at one sun) in solid dye solar cells. In addition, aconcept was presented, in which polymeric p-semiconductors are bondeddirectly to an Ru dye (Peter, K., Appl. Phys. A. 2004, 79, 65). Durrantet al. Adv. Munc. Mater. 2006, 16, 1832-1838 state that, in many cases,the photocurrent is directly dependent on the yield at the holetransition from the oxidized dye to the solid p-conductor. This dependson two factors: firstly on the degree of penetration of thep-semiconductor into the oxide pores, and secondly on the thermodynamicdriving force for the charge transfer (i.e. especially the difference inthe free enthalpy AG between dye and p-conductor).

One disadvantage of the dye solar cell is that the proportion of lightwhich can be used by the dye is generally limited by the energeticdistance between the Fermi energies of the n- and p-conductors used. Thephotovoltage is generally also limited by this distance.

In addition, dye solar cells generally have to be comparatively thin dueto the charge transport required (for example 1-2.5 micrometers), suchthat the exploitation of the incident light is generally not optimal.

The prior art discloses that the addition of silver nitrate (AgNO₃) tothe dye solution can lead to a rise in the solar cell efficiency (J.Krueger, Thesis, EPFL Lausanne, 2003 (Thesis No. 2793), p. 76-100). Thegeneral use of silver in oxidized form as a dopant for thep-semiconductor is not described.

The electric and photoelectric properties of dye solar cells withdifferent low molecular weight p-semiconductors has been examined invarious further studies. One example thereof can be found in U. Bach,thesis, EPFL Lausanne, 2000 (Thesis No. 2187), and therein especially atpages 139-149. One feature examined here is the conductivity ofspiro-MeOTAD, which is very low. For instance, in films with a layerthickness of approx. 2 micrometers, resistivities of MΩ/cm² weremeasured. The conductivity κ is defined by

κ=μN_(h)e  (1)

In this formula, e=1.6022×10⁻¹⁹ C, the elementary charge of an electronor hole. μ denotes the charge carrier mobility, and N_(h) the chargedensity, in this case of the holes. Assuming that the mobility does notchange, in the case of a p-material, the conductivity rises as a resultof the addition of further holes, i.e. in the case of p-doping. Theresult of this is that the fill factors of sDSCs are not very high, inparticular at light intensities which are not low. The fill factor inphotovoltaics generally refers to the quotient of the maximum power of asolar cell at the point of maximum power and the product of theopen-circuit voltage and the short-circuit current. In thecurrent-voltage diagram, the fill factor can frequently be described asthe area ratio of a maximum rectangle inscribed below thecurrent-voltage curve to a minimum rectangle which encloses the curve.The fill factor is unitless. A low fill factor generally indicates thatsome of the power generated is being lost because of the internalresistance of the cell. In the above-described case of spiro-MeOTAD, thecomparatively low fill factors are thus explained especially by the highspecific resistivity of the spiro-MeOTAD, as also described, forexample, in F. Fabregat-Santiago et at., J. Am. Chem. Soc., 2009, 131(2), 558-562, especially at an illumination of one sun.

The prior art also discloses doping of low molecular weight organicp-semiconductors. For example, in U. Bach, thesis, EPFL Lansanne, 2000(Thesis No. 2187), p. 37-50, antimony salts are used as dopants forspiro-MeOTAD. The doping operation can be described chemically asfollows:

[N(p-C₆H₄Br)₃]⁺[SbCl₆]⁻+spiro-MeOTAD→[N(p-C₆H₄Br)₃]+[SbCl₆]⁻+spiro-MeOTAD⁺

A concentration of 0.26-0.33 mM Sb was used, with a proportion of0.17-0.18 M of spiro compounds. Even though the conductivity rises, thehole mobility was reduced as a result of the addition of the anions,which worsen the charge transport. In addition, the stability of suchantimony salts in the cells was questioned.

N. Rossier-Iten, thesis, EPFL Lausanne, 2006 Thesis No. 3457),especially p. 56-75 and p. 91-113, also examined various doped holeconductor materials. The dopants used for an amorphous hole conductor insDSCs therein included I₂, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone,NOBF₄, and also a doped spiro diradical cation (spiro-MeOTAD⁺⁺[PF₆-]₂(0.1-0.7%). However, a decisive improvement in the sDSC cells was notachieved.

In Snaith et al., Appl. Phys. Lett. 2006, 89, 262114-262116, it wasfound that the mobilities of holes in sDSCs are greatly improved by theaddition of lithium bis(trifluoromethylsulfonyl)amine (Li-TFSI). Thus,it was possible to increase the mobilities from 1.6×10⁻⁴ cm²/Vs to1.6×10⁻³ cm²/Vs, even though no oxidation of spiro-MeOTAD is observedhere, i.e. no actual doping effect. It was found that the conductivityof spiro-MeOTAD is influenced to a lesser extent by the antimony salt,and that the best sDSC cells are even achieved without such a salt,since the anions act as what are called Coulomb traps (charge carriertraps).

Typically, an amount of more than 1 mol % of dopant is required in orderto improve the charge mobility of an amorphous p-conductor.

Organic p-dopants, for example F4-TCNQ(tetrafluorotetracyanoquinodimethane) have also already been used withorganic polymers of the p type (see, for example, R. Friend et al, Adv.Mater., 2008, 20, 3319-3324, Zhang et al, Adv. Funct. Mater., 2009, 19,1901-1905). What is called protic doping of polythiophene byalkylsilanes has also been reported (see Podzorov et al., AdvancedFunctional Materials 2009, 19, 1906-1911). Components with organicdopants, however, have comparatively low lifetimes in many cases.

It is additionally known that SnCl₅ and FeCl₃ are also usable asp-dopants. In addition, polymers, such as PEDOT, doped with LiCF₃SO₃,LiBF₄, LiTFSI and LiClO₄, for example, have also been used as holeconductors in sDSCs. In the case of such components too, however,comparatively low external power efficiencies of up to 2.85% wererecorded (Yanagida et al., JACS, 2008, 130, 1258-1263).

In addition, the use of metal oxides as dopants is also known from theprior art, for example from DE 10 2007 024 153 A1 or DE 10 2007 023 876A1. Metal oxides are vapor-deposited in organic layers and serve asdopants therein. An example mentioned is that of phenanthrolinederivatives as a complex-forming matrix material, which are doped, forexample, with rhenium oxides.

In addition, studies on the doping of organic p-transport materials fororganic light-emitting diodes by means of vapor-deposited inorganiccompounds are also known, for example from Kim et al, Appl. Phys. Lett.2007, 91, 011113(1-3). Here, for example, NPB was doped with ReO₃(8-25%), which led to lower use voltages (turn-on voltages) and higherpower efficiencies. The stability of the OLEDs was likewise improved.Kim et al., Org. Elec. 2008, 805-808 state that hole injection layershave been doped with CuI. This doping too led to higher currentefficiencies and energy efficiencies. Kim et al., Appl. Phys. Lett.2009, 94, 123306 (1-3) compare CuI, MoO₃ and ReO₃ as dopants for organiclight-emitting diodes (OLEDs) A trend is found here to the effect thatthe energy difference between the HOMO (highest occupied molecularorbital) of the organic p-semiconductor and the Fermi level of thedopants plays an important role. Overall, it was found that the dopantsincrease the charge carrier densities and hence the conductivities inthe transport layers, which is equivalent to p-doping.

Kahn et al., Chem. Mater. 2010, 22, 524-531 also discloses thatmolybdenum dithiolene (Mo(tfd)₃) in a concentration of 0-3.8 mol % candope various hole conductors. By means of UPS experiments (UVphotoelectron spectroscopy), it was shown that the Fermi level of thehole conductor has been shifted in the direction of the HOMO, which isan indication of p-doping.

Kowalsky et al., Org. Elec. 2009, 10, 932-938 report that Mo₃O₉ clustersof vapor-deposited MoO₃ probably arise, and can also play a role indoping. In addition, the Fermi level (6.86 eV) and the electron affinity(6.7 eV) were measured at a much lower level that previously assumed. Itwas also speculated (cf. Kanai et al., Organic Electronics 2010, 11,188-194) that MoO₃ layers can readily be n-doped by oxygen defect sites,which leads to an improved alignment of the bands with respect to oneanother.

The use of pure layers of metal oxides, for example MoO₃ and V₂O₅, isalso described for OLEDs and for organic solar cells, in order toimprove hole injection or hole extraction from the/into the electrode.For example, Y. Yang et al, Appl. Phys. Lett. 2006, 88, 073508 examinethe use of V₂O₅, MoO₃ and PEDOT:PSS as an intermediate layer between ITO(indium tin oxide) and a p-type polymer. In what are called invertedpolymer cells too, in which holes should migrate from the p-type polymerinto the cathode (in this case generally Ag), a VOx layer wasvapor-deposited between the polymer and the silver, which led to animprovement in the properties of the cell.

In addition, the production of metal oxide buffer layers from an aqueoussolution is also known. For example, Liu SESMC, 2010, 842-845, vol. 94states that MoO₃ layers have been used successfully as a buffer layer onthe anode in polymer solar cells. Such layers have also been used aspart of a charge recombination layer in what are called organic tandemsolar cells (see, for example, Kowalsky et al., Adv. Func. Mater. 2010,20, 1762-1766).

Since no efficient, soluble and stable p-dopant for hole transportmaterials is yet known in general terms, in the last few years, dyesolar cells have in practice been stored under air (ambient conditions)in many cases. Oxygen which penetrates into the sDSCs in the coursethereof dopes the sDSC. The storage of cells in an ambient atmosphere orin a controlled O₂ atmosphere is, however, less reproducible andcomparatively problematic with regard to commercial production of solarmodules. In addition, it is impossible to encapsulate oxygen-doped cellsin an airtight manner, since a high conductivity of the whole conductor,which is needed for operation, is ensured only with constant contact tooxygen.

OBJECT OF THE INVENTION

It is therefore an object of the present invention to provide aphotovoltaic element and a process for producing a photovoltaic element,which at least substantially avoid the disadvantages of knownphotovoltaic elements and production processes. More particularly, aphotovoltaic element will be specified, which has a p-semiconductor witha high conductivity, as will a process for doping p-semiconductors and astable p-dopant which, even with exclusion of oxygen, brings aboutstable p-doping of organic materials for dye solar cells. At the sametime, a dye solar cell which is stable even in the encapsulated stateand has a high quantum efficiency and a high fill factor would bedesirable, nevertheless being simple to produce.

DISCLOSURE OF THE INVENTION

This object is achieved by the invention with the features of theindependent claims. Advantageous developments, which can be implementedindividually or in any combination, are described in the dependentclaims.

In a first aspect of the present invention, a photovoltaic element forconversion of electromagnetic radiation to electrical energy isproposed, more particularly a dye solar cell. The photovoltaic elementcomprises at least one first electrode, at least one n-semiconductivemetal oxide, at least one dye which absorbs electromagnetic radiation,at least one solid organic p-semiconductor and at least one secondelectrode, preferably (but not necessarily) in the sequence described ora reverse sequence, the p-semiconductor comprising silver in oxidizedform.

The p-semiconductor may especially be producible or have been producedby applying at least one p-semiconductive organic material (128) andsilver in oxidized form to at least one carrier element, the silver inoxidized form preferably being applied in the form of at least onesilver(I) salt [Ag⁺]_(m)[A^(m−)] to at least one carrier element, whereA^(m−) is the anion of an organic or inorganic acid, and m is an integerin the range from 1 to 3, preferably where m is 1.

[A^(m−)] may especially be an anion of an organic acid, preferably wherethe organic acid has at least one fluorine group —F or cyano group(—CN). In this case, [A^(m−)] more preferably has a structure of theformula (II)

where R^(a) is a fluorine group —F or an alkyl radical, cycloalkylradical, aryl radical or heteroaryl radical each substituted by afluorine group or a cyano group,and where X is —O— or —N⁻—R^(b),and where R^(b) comprises a fluorine group —F or a cyano group,and where R^(b) further comprises a group of the formula —(O)₂ ⁻.

R^(a) may especially be selected from the group consisting of —F, —CF₃,—CF₂—CF₃ and —CH₂—CN.

X may especially be —N⁻—R^(b), and R^(b) may especially be selected fromthe group consisting of —S(O)₂—F, —S(O)₂—CF₃, —S(O)₂—CF₂—CF₃ and—S(O)₂—CH₂—CN.

[A^(m−)] may especially be selected from the group consisting of:bis(trifluoromethylsulfonyl)imide (TFSI⁻),bis(trifluoroethylsulfonyl)imide, bis(fluoro-sulfonyl)imide,trifluoromethylsulfonate.

Preferably, [A^(m−)] is bis(trifluoromethylsulfonyl)imide (TFSI⁻). In analternative preferred embodiment, [A^(m−)] is a trifluoroacetate group.

In addition, [A^(m−)] may especially also be an NO₃ ⁻ group.

The application can be effected by any desired process. Preference isgiven to applying the at least one p-conductive organic material (128)and silver in the context of the invention by deposition from a liquidphase.

The p-semiconductor is preferably producible or produced by applying atleast one p-conductive organic material (128) and at least silver,preferably the at least one silver(I) salt [Ag⁺]_(m)[A^(m−)], to atleast one carrier element, the application being effected by depositionfrom a liquid phase comprising the at least one p-conductive organicmaterial and the at least one silver(I) salt [Ag⁺]_(m)[A^(m−)].

The deposition can again in principle be effected by any desireddeposition process, for example by spin-coating, knife-coating, printingor combinations of said and/or other deposition processes.

The p-semiconductor may especially comprise at least one organic matrixmaterial, in which case the anionic compounds [A^(m−)] and Ag⁺ have beenmixed into the matrix material or are present in the matrix material,especially in dissolved form.

At least Ag⁺ and preferably also the anionic compound [A^(m−)] mayespecially be present in essentially homogeneous distribution in thematrix material.

The matrix material may especially comprise at least one low molecularweight organic p-semiconductor.

The low molecular weight organic p-semiconductor may especially compriseat least one spiro compound.

The low molecular weight organic p-semiconductor may especially beselected from: a spiro compound, especially spiro-MeOTAD; a compoundwith the structural formula:

in whichA¹, A², A³ are each independently optionally substituted aryl groups orheteroaryl groups,R¹, R², R³ are each independently selected from the group consisting ofthe substituents —R, —OR, —NR₂, -A⁴-OR and -A⁴-NR₂,

where R is selected from the group consisting of alkyl, aryl andheteroaryl,

andwhere A⁴ is an aryl group or heteroaryl group, andwhere n at each instance in formula I is independently a value of 0, 1,2 or 3,with the proviso that the sum of the individual n values is at least 2and at least two of the R¹, R² and R³ radicals are —OR and/or —NR₂.

Preferably, A² and A³ are the same; accordingly, the compound of theformula (I) preferably has the following structure (Ia)

The photovoltaic element may further comprise at least oneencapsulation, the encapsulation being designed to shield thephotovoltaic element, especially the electrodes and/or thep-semiconductor, from a surrounding atmosphere.

In a preferred embodiment, the p-semiconductor has been produced or isproducible by applying at least one p-conductive organic material (128)and at least one silver(I) salt [Ag⁺]_(m)[A^(m−)] to at least onecarrier element as described above, wherein the application can beeffected by deposition from a liquid phase comprising the at least onep-conductive organic material and the at least one silver(I) salt[Ag⁺]_(m)[A^(m−)], and wherein the liquid phase comprises the at leastone silver(I) salt [Ag⁺]_(m)[A^(m−)] in a concentration of 0.5 mm/ml to50 mm/ml, more preferably in a concentration of 1 mm/ml up to 20 mm/ml.

In a further aspect of the present invention, a process for producing asolid organic p-semiconductor for use in an organic component isproposed, more particularly a photovoltaic element according to one ormore of the embodiments of a photovoltaic element according to thepresent invention which have been described above or are yet to bedescribed. In the process, at least one p-conductive organic matrixmaterial and at least silver in oxidized form, preferably at least onesilver(I) salt [Ag⁺]_(m)[A^(m−)], are applied from at least one liquidphase to at least one carrier element, where [A]⁻ is the anion of anorganic or inorganic acid, and where the compound [Ag⁺]_(m)[A^(m−)] ispreferably AgNO₃ or silver bis(trifluoromethylsulfonyl)imide.

The liquid phase may further comprise at least one solvent, especiallyan organic solvent, especially a solvent selected from the groupconsisting of cyclohexanone; chlorobenzene; benzofuran andcyclopentanone.

The process can especially be performed at least partly in a low-oxygenatmosphere, for example in an atmosphere comprising less than 500 ppm ofoxygen, especially less than 100 ppm of oxygen and more preferably lessthan 50 ppm or even less than 10 ppm of oxygen.

In a further aspect of the present invention, a process for producing aphotovoltaic element is proposed, especially a photovoltaic elementaccording to one or more of the configurations of a photovoltaic elementaccording to the present invention which have been described above orare yet to be described. In the process, at least one first electrode,at least one n-semiconductive metal oxide, at least one dye whichabsorbs electromagnetic radiation, at least one solid organicp-semiconductor and at least one second electrode are provided,especially (but not necessarily) in the sequence described or a reversesequence, the p-semiconductor being produced by a process according toone or more of the configurations of a process according to theinvention for producing a solid organic p-semiconductor which have beendescribed above or are yet to be described.

It has been found in the context of the present invention that,surprisingly, silver in oxidized form can achieve efficient p-doping,especially in dye solar cells. Particularly efficient p-doping can beachieved especially by the use of a silver(I) salt of the formula[Ag⁺]_(m)[A^(m−)] where [A^(m−)] is the anion of an organic or inorganicacid, and m is an integer in the range from 1 to 3. These silver(I)salts can be applied especially in a liquid phase by means of one ormore organic solvents, preferably together with a p-semiconductivematrix material and optionally one or more organic salts. In this way,it is possible to achieve photovoltaic elements with high fill factorsand a high long-term stability.

In the abovementioned first aspect of the present invention, aphotovoltaic element for conversion of electromagnetic radiation toelectrical energy is thus proposed. The photovoltaic element mayespecially comprise one or more photovoltaic cells. The photovoltaicelement may especially comprise at least one layer structure which maybe applied, for example, to a substrate. The photovoltaic element mayespecially comprise at least one dye solar cell and/or be configured asa dye solar cell.

The photovoltaic element has at least one first electrode, at least onen-semiconductive metal oxide, at least one electromagneticradiation-absorbing dye, at least one solid organic p-semiconductor andat least one second electrode. It is proposed that the p-semiconductorcomprises silver in oxidized form.

The elements described may be provided especially in the sequencedescribed. For example, the photovoltaic element may comprise, in thesequence described, the at least one first electrode, the at least onen-semiconductive metal oxide, the at least one electromagneticradiation-absorbing dye, the at least one solid organic p-semiconductorand the at least one second electrode. However, the dye and then-semiconductive metal oxide may also be completely or partiallycombined, as is customary in dye solar cells. For example, then-semiconductive metal oxide may be completely or partially impregnatedwith the at least one dye, or mixed with this dye in some other way. Inthis way and/or in some other way, the n-semiconductive metal oxide canespecially be sensitized with the dye, such that, for example, dyemolecules can be applied as a monolayer to particles of then-semiconductive metal oxide. For example, a direct contact may existbetween the dye molecules and the n-semiconductive metal oxide, suchthat transfer of charge carriers is possible. The photovoltaic elementmay especially comprise at least one layer of the n-semiconductive metaloxide, optionally with the dye, and at least one layer of the solidorganic p-semiconductor. This layer structure may be embedded betweenthe electrodes. In addition, the photovoltaic element may comprise oneor more further layers. For example, one or more further layers may beintroduced between the first electrode and the n-semiconductive metaloxide, for example one or more buffer layers, for example layers of ametal oxide. While the buffer layer is preferably impervious, then-semiconductive metal oxide may especially be porous and/orparticulate. More particularly, the n-semiconductive metal oxide, aswill be described in detail hereinafter, may be configured as ananoparticulate layer. In addition, it is also possible for one or morefurther layers to be provided between the n-semiconductive metal oxideand the solid organic p-semiconductor, and also optionally for one ormore further layers to be provided between the p-semiconductor and thesecond electrode.

The p-semiconductor may especially be p-doped by the silver in oxidizedform, preferably by the at least one silver(I) salt of the formula[Ag⁺]_(m)[A^(m−)]. This means that the p-conductive properties of thep-semiconductor are obtained or enhanced by the silver in oxidized form,preferably by the at least one silver(I) salt of the formula[Ag⁺]_(m)[A^(m−)]. More particularly, the silver in oxidized form,especially the at least one silver(I) salt of the formula[Ag⁺]_(m)[A^(m−)], may be set up to dope the p-semiconductor or a matrixmaterial present in this p-semiconductor. For example, thep-semiconductor may comprise at least one organic matrix material, inwhich case the silver in oxidized form, preferably the at least onesilver(I) salt of the formula [Ag⁺]_(m)[A^(m−)], has been mixed into thematrix material. This is preferably achieved by applying both silver inoxidized form, preferably at least one silver(I) salt of the formula[Ag⁺]_(m)[A^(m−)], and the organic matrix material to at least onecarrier material.

Accordingly, the present invention preferably relates to a photovoltaicelement as described above, wherein the p-semiconductor is producible orhas been produced by applying at least one p-conductive organic material(128) and silver in oxidized form to at least one carrier element, thesilver in oxidized form preferably being applied in the form of at leastone silver(I) salt [Ag⁺]_(m)[A^(m−)] to at least one carrier element,where A^(m−) is the anion of an organic or inorganic acid, and m is aninteger in the range from 1 to 3, preferably where m is 1.

The matrix material and the silver may be applied to the carriermaterial together or in separate steps. Preferably, the matrix materialand the silver are applied together to the carrier material. “Appliedtogether” or “applied jointly” in this context means that preferably amixture G comprising both the matrix material is applied to the carriermaterial in at least one step, preferably in one step.

Preferably, the mixture G is a liquid phase. The term “liquid phase” inthis context means that mixture G is present at least partly as aliquid. Preferably, mixture G or preferably the liquid phase comprisesat least one solvent in which silver and the at least one organic matrixmaterial are dissolved and/or dispersed, as described below. As alreadystated above, the application is preferably effected by deposition fromthe liquid phase, and the deposition can again in principle be effectedby any desired deposition process, for example by spin-coating,knife-coating, printing or combinations of said and/or other depositionprocesses.

The Low Molecular Weight Organic P-Semiconductor:

More particularly, the matrix material may have at least one lowmolecular weight organic p-semiconductor. A low molecular weightmaterial is generally understood to mean a material which is present inmonomeric, nonpolymerized or nonoligomerized form. The term “lowmolecular weight” as used in the present context preferably means thatthe semiconductor has molecular weights in the range from 100 to 25 000g/mol. Preferably, the low molecular weight substances have molecularweights of 500 to 2000 g/mol. These low molecular weight organicp-semiconductors may especially form the abovementioned matrix materialand may intrinsically have p-semiconductive properties. In general, inthe context of the present invention, p-semiconductive properties areunderstood to mean the property of materials, especially of organicmolecules, to form holes and to transport these holes and to pass themon to adjacent molecules. More particularly, stable oxidation of thesemolecules should be possible. In addition, the low molecular weightorganic p-semiconductors mentioned may especially have an extensiveπ-electron system. More particularly, the at least one low molecularweight p-semiconductor may be processable from a solution. The lowmolecular weight p-semiconductor may especially comprise at least onetriphenylamine. It is particularly preferred when the low molecularweight organic p-semiconductor comprises at least one spiro compound. Aspiro compound is understood to mean polycyclic organic compounds whoserings are joined only at one atom, which is also referred to as thespiro atom. More particularly, the spiro atom may be sp³-hybridized,such that the constituents of the spiro compound connected to oneanother via the spiro atom are, for example, arranged in differentplanes with respect to one another.

More preferably, the spiro compound has a structure of the followingformula:

where the aryl¹, aryl², aryl³, aryl⁴, aryl⁵, aryl⁶, aryl⁷ and aryl⁸radical are each independently selected from substituted aryl radicalsand heteroaryl radicals, especially from substituted phenyl radicals,where the aryl radicals and heteroaryl radicals, preferably the phenylradicals, are each independently substituted, preferably in each case byone or more substituents selected from the group consisting of —O-alkyl,—OH, —F, —Cl, —Br and —I, where alkyl is preferably methyl, ethyl,propyl or isopropyl. More preferably, the phenyl radicals are eachindependently substituted, in each case by one or more substituentsselected from the group consisting of —O—Me, —OH, —F, —Cl, —Br and —I.

Further preferably, the spiro compound is a compound of the followingformula:

where R^(r), R^(s), R^(t), R^(u), R^(v), R^(w), R^(x) and R^(y) are eachindependently selected from the group consisting of —O-alkyl, —OH, —F,—Cl, —Br and —I, where alkyl is preferably methyl, ethyl, propyl orisopropyl. More preferably, R^(r), R^(s), R^(t), R^(u), R^(v), R^(w),R^(x) and R^(y) are each independently selected from the groupconsisting of —O—Me, —OH, —F, —Cl, —Br and —I.

More particularly, the p-semiconductor or the matrix material maycomprise spiro-MeOTAD or consist of spiro-MeOTAD, i.e. a compound of theformula (III) commercially available, for example, from Merck KGaA,Darmstadt, Germany, Taiwan:

Alternatively or additionally, it is also possible to use otherp-semiconductive compounds, especially low molecular weight and/oroligomeric and/or polymeric p-semiconductive compounds.

In an alternative embodiment, the low molecular weight organicp-semiconductor or the matrix material comprises one or more compoundsof the abovementioned general formula I, for which reference may bemade, for example, to PCT application number PCT/EP2010/051826, whichwill be published after the priority date of the present application.

The p-semiconductor may comprise the at least one compound of theabove-mentioned general formula I additionally or alternatively to thespiro compound described above.

The term “alkyl” or “alkyl group” or “alkyl radical” as used in thecontext of the present invention is understood to mean substituted orunsubstituted C₁-C₂₀-alkyl radicals in general. Preference is given toC₁- to C₈-alkyl radicals, particular preference to C₁- to C₈-alkylradicals. The alkyl radicals may be either straight-chain or branched.In addition, the alkyl radicals may be substituted by one or moresubstituents selected from the group consisting of C₁-C₂₀-alkoxy,halogen, preferably F, and C₆-C₃₀-aryl which may in turn be substitutedor unsubstituted. Examples of suitable alkyl groups are methyl, ethyl,propyl, butyl, pentyl, hexyl, heptyl and octyl, and also isopropyl,isobutyl, isopentyl, sec-butyl, tert-butyl, neopentyl,3,3-dimethylbutyl, 2-ethylhexyl, and also derivatives of the alkylgroups mentioned substituted by C₆-C₃₀-aryl, C₁-C₂₀-alkoxy and/orhalogen, especially F, for example CF₃.

The term “aryl” or “aryl group” or “aryl radical” as used in the contextof the present invention is understood to mean optionally substitutedC₆-C₃₀-aryl radicals which are derived from monocyclic, bicyclic,tricyclic or else multicyclic aromatic rings, where the aromatic ringsdo not comprise any ring heteroatoms. The aryl radical preferablycomprises 5- and/or 6-membered aromatic rings. When the aryls are notmonocyclic systems, in the case of the term “aryl” for the second ring,the saturated form (perhydro form) or the partly unsaturated form (forexample the dihydro form or tetrahydro form), provided the particularforms are known and stable, is also possible. The term “aryl” in thecontext of the present invention thus comprises, for example, alsobicyclic or tricyclic radicals in which either both or all threeradicals are aromatic, and also bicyclic or tricyclic radicals in whichonly one ring is aromatic, and also tricyclic radicals in which tworings are aromatic. Examples of aryl are: phenyl, naphthyl, indanyl,1,2-dihydronaphthenyl, 1,4-dihydronaphthenyl, fluorenyl, indenyl,anthracenyl, phenanthrenyl or 1,2,3,4-tetrahydronaphthyl. Particularpreference is given to C₆-C₁₀-aryl radicals, for example phenyl ornaphthyl, very particular preference to C₆-aryl radicals, for examplephenyl. In addition, the term “aryl” also comprises ring systemscomprising at least two monocyclic, bicyclic or multicyclic aromaticrings joined to one another via single or double bonds. One example isthat of biphenyl groups.

The term “heteroaryl” or “heteroaryl group” or “heteroaryl radical” asused in the context of the present invention is understood to meanoptionally substituted 5- or 6-membered aromatic rings and multicyclicrings, for example bicyclic and tricyclic compounds having at least oneheteroatom in at least one ring. The heteroaryls in the context of theinvention preferably comprise 5 to 30 ring atoms. They may bemonocyclic, bicyclic or tricyclic, and some can be derived from theaforementioned aryl by replacing at least one carbon atom in the arylbase skeleton with a heteroatom. Preferred heteroatoms are N, O and S.The hetaryl radicals more preferably have 5 to 13 ring atoms. The baseskeleton of the heteroaryl radicals is especially preferably selectedfrom systems such as pyridine and five-membered heteroaromatics such asthiophene, pyrrole, imidazole or furan. These base skeletons mayoptionally be fused to one or two six-membered aromatic radicals. Inaddition, the term “heteroaryl” also comprises ring systems comprisingat least two monocyclic, bicyclic or multicyclic aromatic rings joinedto one another via single or double bonds, where at least one ringcomprises a heteroatom. When the heteroaryls are not monocyclic systems,in the case of the term “heteroaryl” for at least one ring, thesaturated form (perhydro form) or the partly unsaturated form (forexample the dihydro form or tetrahydro form), provided the particularforms are known and stable, is also possible. The term “heteroaryl” inthe context of the present invention thus comprises, for example, alsobicyclic or tricyclic radicals in which either both or all threeradicals are aromatic, and also bicyclic or tricyclic radicals in whichonly one ring is aromatic, and also tricyclic radicals in which tworings are aromatic, where at least one of the rings, i.e. one aromaticor one nonaromatic ring has a heteroatom. Suitable fused heteroaromaticsare, for example, carbazolyl, benzimidazolyl, benzofuryl, dibenzofurylor dibenzothiophenyl. The base skeleton may be substituted at one, morethan one or all substitutable positions, suitable substituents being thesame as have already been specified under the definition of C₆-C₃₀-aryl.However, the hetaryl radicals are preferably unsubstituted. Suitablehetaryl radicals are, for example, pyridin-2-yl, pyridin-3-yl,pyridin-4-yl, thiophen-2-yl, thiophen-3-yl, pyrrol-2-yl, pyrrol-3-yl,furan-2-yl, furan-3-yl and imidazol-2-yl and the correspondingbenzofused radicals, especially carbazolyl, benzimidazolyl, benzofuryl,dibenzofuryl or dibenzothiophenyl.

In the context of the invention the term “optionally substituted” refersto radicals in which at least one hydrogen radical of an alkyl group,aryl group or heteroaryl group has been replaced by a substituent. Withregard to the type of this substituent, preference is given to alkylradicals, for example methyl, ethyl, propyl, butyl, pentyl, hexyl,heptyl and octyl, and also isopropyl, isobutyl, isopentyl, sec-butyl,tert-butyl, neopentyl, 3,3-dimethylbutyl and 2-ethylhexyl, arylradicals, for example C₆-C₁₀-aryl radicals, especially phenyl ornaphthyl, most preferably C₆-aryl radicals, for example phenyl, andhetaryl radicals, for example pyridin-2-yl, pyridin-3-yl, pyridin-4-yl,thiophen-2-yl, thiophen-3-yl, pyrrol-2-yl, pyrrol-3-yl, furan-2-yl,furan-3-yl and imidazol-2-yl, and also the corresponding benzofusedradicals, especially carbazolyl, benzimidazolyl, benzofuryl,dibenzofuryl or dibenzothiophenyl. Further examples include thefollowing substituents: alkenyl, alkynyl, halogen, hydroxyl.

The degree of substitution here may vary from monosubstitution up to themaximum number of possible substituents.

Preferred compounds of the formula I for use in accordance with theinvention are notable in that at least two of the R¹, R² and R³ radicalsare para-OR and/or —NR₂ substituents. The at least two radicals here maybe only —OR radicals, only —NR₂ radicals, or at least one —OR and atleast one —NR₂ radical.

Particularly preferred compounds of the formula I for use in accordancewith the invention are notable in that at least four of the R¹, R² andR³ radicals are para-OR and/or —NR₂ substituents. The at least fourradicals here may be only —OR radicals, only —NR₂ radicals or a mixtureof —OR and —NR₂ radicals.

Very particularly preferred compounds of the formula I for use inaccordance with the invention are notable in that all of the R¹, R² andR³ radicals are para-OR and/or —NR₂ substituents. They may be only —ORradicals, only —NR₂ radicals or a mixture of —OR and —NR₂ radicals.

In all cases, the two R in the —NR₂ radicals may be different from oneanother, but they are preferably the same.

Preferably, A¹, A² and A³ are each independently selected from the groupconsisting of

in which

-   m is an integer from 1 to 18,-   R⁴ is alkyl, aryl or heteroaryl, where R⁴ is preferably an aryl    radical, more preferably a phenyl radical,-   R⁵, R⁶ are each independently H, alkyl, aryl or heteroaryl,    where the aromatic and heteroaromatic rings of the structures shown    may optionally have further substitution. The degree of substitution    of the aromatic and heteroaromatic rings here may vary from    monosubstitution up to the maximum number of possible substituents.

Preferred substituents in the case of further substitution of thearomatic and heteroaromatic rings include the substituents alreadymentioned above for the one, two or three optionally substitutedaromatic or heteroaromatic groups.

Preferably, the aromatic and heteroaromatic rings of the structuresshown do not have further substitution.

More preferably. A¹, A² and A³ are each independently

more preferably

More preferably, the at least one compound of the formula (I) has one ofthe following structures:

In an alternative embodiment, the matrix material is ID322, i.e. acompound of the formula (IV):

The compounds for use in accordance with the invention can be preparedby customary methods of organic synthesis known to those skilled in theart. References to relevant (patent) literature can additionally befound in the synthesis examples adduced below.

At least one of the electrodes may be transparent. For example, thefirst electrode may be the working electrode and the second electrodethe counterelectrode, or vice versa. One or both of these electrodes maybe transparent. The photovoltaic element may especially comprise atleast one layer structure applied to a substrate, in which case thelayer structure may comprise the first electrode, the n-semiconductivemetal oxide, the dye, the solid organic p-semiconductor with the metaloxide and the at least one second electrode in the sequence mentioned,or in reverse sequence.

The n-semiconductive metal oxide may especially be porous, in whichcase, at least one buffer layer of a metal oxide may especially beintroduced between the n-semiconductive metal oxide and the firstelectrode. This buffer layer may be, for example, an impervious layer,i.e. a nonparticulate layer. For example, this buffer layer may beapplied by means of a PVD process, for example a vapor depositionprocess and/or a sputtering process. Alternatively or additionally, itis also possible to use other processes, for example CVD processesand/or spray pyrolysis processes. The n-semiconductive metal oxide is,in contrast, preferably applied by means of a paste process, for exampleby print application, spin-coating application or knife-coatingapplication of a paste of an n-semiconductive metal oxide. This pastecan subsequently be sintered by at least one thermal treatment step, forexample by heating to more than 200° C., especially to more than 400°C., for example 450° C. This sintering can, for example, remove volatileconstituents of the paste, such that preferably only then-semiconductive metal oxide particles remain.

As described above, the dye can especially be applied to then-semiconductive metal oxide. This application is preferably effected insuch a way that the dye completely or partially penetrates ann-semiconductive metal oxide layer, for example a particulate layer, inorder to sensitize the particles of the n-semiconductive metal oxide,for example by virtue of one or more layers of the dye being formed onthese particles, for example monomolecular layers. The application ofthe dye can accordingly be effected, for example, by means of at leastone impregnation process, by, for example, immersing a sample comprisingthe n-semiconductive metal oxide layer into a solution of the dye. Otherimpregnation processes are also usable.

As a particular advantage of the present invention, the photovoltaicelement may especially comprise at least one encapsulation. In contrastto conventional photovoltaic elements, in which solid p-semiconductorsare doped by means of oxygen (for example by storage under air), thep-semiconductors doped with the silver in oxidized form, for example theat least one silver(I) salt [Ag⁺]_(m)[A^(m−)] and especially preferablysilver bis(trifluoromethylsulfonyl)imide, may also exist without such anoxygen atmosphere over a prolonged period. Accordingly, it is possibleto apply an encapsulation which screens the photovoltaic element,especially the electrodes and/or the p-semiconductor, from a surroundingatmosphere. In this way, in spite of the improvement in properties ofthe p-semiconductor by virtue of the doping by means of the silver inoxidized form, especially the at least one silver(I) salt[Ag⁺]_(m)[A^(m−)] and especially preferably silverbis(trifluoromethylsulfonyl)imide, oxygen can be excluded, whichprotects, for example, one or more of the electrodes from adverseeffects resulting from oxygen and/or other surrounding gases. Forexample, the electrode degradation can be prevented in this way. Theencapsulation may, for example, comprise encapsulation by a solidcapsule element, for example a plane or capsule equipped with at leastone depression, which is applied to the layer structure, for example, insuch a way that it completely or partially surrounds the layerstructure. For example, an edge of the encapsulation may completely orpartially surround the layer structure and, for example, may be bondedto the substrate by an adhesive bond and/or another bond, preferably acohesive bond. Alternatively or additionally, the encapsulation may alsocomprise one or more layers of a material which prevents penetration ofharmful environmental influences, for example moisture and/or oxygen.For example, organic and/or inorganic coatings can be applied to thelayer structure. Screening from ambient atmosphere can generally beunderstood to mean slowing of the penetration of gases and/or moisturefrom the surrounding atmosphere into the layer structure. The slowingcan be effected, for example, in such a way that concentrationdifferences within and outside the encapsulation are balanced out onlywithin several hours, preferably several days, especially even severalweeks, months extending up to years.

The dye solar cell may additionally have, between the n-semiconductivemetal oxide and the p-semiconductor, especially at least one passivationmaterial. This passivation material may especially be set up to at leastpartly prevent electron transfer between the n-semiconductive metaloxide and the p-semiconductor. The passivation material may especiallybe selected from: Al₂O₃; a silane, especially CH₃SiCl₃; anorganometallic complex, especially an Al³⁺ complex, a4-tert-butylpyridine; hexadecylmalonic acid.

As detailed above, in a further aspect of the present invention, aprocess is proposed for producing a solid organic p-semiconductor foruse in an organic component. This organic component may especially be aphotovoltaic element, for example a photovoltaic element in one or moreof the above-described configurations, especially a dye solar cell.However, other configurations of the organic component are also possiblein principle, including the end use in organic light-emitting diodes,organic transistors, and other types of photovoltaic elements, forexample organic solar cells.

In the process proposed, at least one p-conductive organic matrixmaterial, for example a matrix material of the type described above, andat least silver in oxidized form, preferably at least one silver(I) saltof the formula [Ag⁺]_(m)[A^(m−)], are applied to at least one carrierelement from at least one liquid phase. As described above, ap-conductive organic matrix material is understood to mean an organicmaterial which can preferably be applied from solution and which iscapable of transporting positive charges. These positive charges mayalready be present in the matrix material and merely be increased by thep-doping, or can also actually be obtained as a result of the p-dopingby means of the silver in oxidized form. More particularly, the matrixmaterial may be stably and reversibly oxidizable and be set up to passpositive charges (“holes”) on to other molecules, for example adjacentmolecules of the same type.

In general, it is pointed out in this regard that the effect of thesilver salt is based merely on observable effects of an increase in thep-conductivity. Accordingly, it is possible, for example, to increase acharge carrier density and/or a mobility of positive charges in thep-semiconductor by addition of the silver in oxidized form. Theinvention is not limited to the way in which the p-doping is effected atthe microscopic level.

The at least one organic matrix material and the silver in oxidizedform, especially the at least one silver(I) salt of the formula [Ag^(+])_(m)[A^(m−)], as a p-dopant are preferably applied together to the atleast one carrier element from at least one liquid phase, as describedabove. A carrier element may be understood to mean a pure substrate, forexample a glass and/or plastic and/or laminate substrate. Alternativelyor additionally, the carrier element may, however, also comprise furtherelements, for example one or more electrodes and/or one or more layers,which may already be applied to the substrate. For example, thep-semiconductor can be applied from the liquid phase to an alreadypartially or completely finished layer structure, in which case, forexample, one or more layers may already be applied to a substrate, andthen at least one layer of the p-semiconductor is applied. For example,the at least one first electrode, the at least one n-semiconductivemetal oxide and preferably the dye may already be applied to asubstrate, as described above with regard to the photovoltaic element,before the p-semiconductor is applied from the at least one liquidphase.

Application from a liquid phase may generally comprise, for example, awet chemical processing operation, for example a spin-coating,knife-coating, casting, printing or similar wet chemical processes orcombinations of the processes mentioned and/or other processes. Forexample, it is possible to use printing processes such as inkjetprinting, screen printing, offset printing or the like. The applicationfrom the liquid phase may especially be followed by drying of thep-semiconductor, for example in order to remove volatile constituentssuch as solvents of the liquid phase. This drying can be effected, forexample, under thermal action, for example at temperatures of 30° C. to150° C. Other configurations are, however, also possible in principle.

The matrix material may especially, as described above, comprise atleast one low molecular weight organic p-semiconductor, for example asmatrix material. More particularly, it is possible to use one or more ofthe above-described organic p-semiconductors. More particularly, the lowmolecular weight organic p-semiconductor may comprise at least onetriphenylamine. The low molecular weight organic p-semiconductor mayespecially comprise at least one spiro compound, for example one or moreof the above-described spiro compounds.

The liquid phase may, in addition to the at least one matrix materialand the silver in oxidized form, especially the at least one silver(I)salt of the formula [Ag⁺]_(m)[A^(m−)], further comprise one or moreadditional components which may have different end uses. For example, itis known for stabilization purposes and/or for improvement of theelectrical properties to use spiro compounds, for example spiro-MeOTAD,in solution with at least one lithium salt. In general, the liquid phasemay accordingly further comprise, for example, at least one metal salt.More particularly, this may be an organometallic salt. A combination ofdifferent salts is also possible. More particularly, it is possible touse lithium salts, for example organometallic lithium salts, preferablyLiN(SO₂CF₃)₂.

As described above, the at least one liquid phase may especiallycomprise at least one solvent. The term “solvent” is used here, in thecontext of the present invention, irrespective of whether all, severalor individual constituents present in the liquid phase are actuallypresent in dissolved form or whether they are present in another form,for example as a suspension, dispersion, emulsion or in some other form.More particularly, the silver in oxidized form, for example the at leastone silver(I) salt [Ag⁺]_(m)[A^(m−)] and especially preferably silverbis(trifluoromethylsulfonyl)imide may be present in dissolved form. Forexample, the at least one matrix material may be present in dissolved orelse in dispersed form. The silver in oxidized form, for example the atleast one silver(I) salt [Ag⁺]_(m)[A^(m−)] and especially preferablysilver bis(trifluoromethylsulfonyl)imide may especially be present indissolved form, but may also in principle be present in another form,for example in dispersed and/or suspended form.

Particular preference is given to the use of at least one organicsolvent. More particularly, it is possible to use one or more of thefollowing solvents: cyclohexanone; chlorobenzene; benzofuran;cyclopentanone.

The proposed process for producing a solid organic p-semiconductor canespecially be used to produce the above-described photovoltaic elementin one or more of the configurations described. However, other organiccomponents are also producible by means of the process. A combinationwith other known processes is also conceivable in principle, and so, forexample, when a plurality of organic p-semiconductors are provided, oneor more of these p-semiconductors are producible by means of theproposed process according to the invention, and one or more of theconventional p-semiconductors by means of other processes.

A particular advantage of the proposed process for producing the solidorganic p-semiconductor is that—in contrast to many processes known fromthe prior art—storage under air is not necessarily required. Forinstance, the process may especially be performed at least partly in alow-oxygen atmosphere. In the context of the present invention, anorganic component is generally understood to mean a component which hasone or more organic elements, for example one or more organic layers. Itis possible to use entirely organic components, for example componentsin which the layer structure—optionally with the exception of theelectrodes—comprises only organic layers. However, it is also possibleto produce hybrid components, for example components which comprise, aswell as one or more organic layers, one or more inorganic layers. Whenthe process proposed is used to produce the solid organicp-semiconductor in a multistep production process, it is possible toperform one, more than one or all of the process steps for production ofthe organic component in a low-oxygen atmosphere. More particularly, theprocess step of production of the solid organic p-semiconductor can beperformed in the low-oxygen atmosphere, in contrast to theabove-described known processes. More particularly, the application ofthe liquid phase to the carrier element can thus be performed in thelow-oxygen atmosphere. A low-oxygen atmosphere is generally understoodto mean an atmosphere which has a reduced oxygen content compared to theambient air. For example, the low-oxygen atmosphere may have an oxygencontent of less than 1000 ppm, preferably of less than 500 ppm and morepreferably of less than 100 ppm, for example 50 ppm or less. It is alsopossible to perform further processing of the organic component, forexample of the dye solar cell, under such a low-oxygen atmosphere. Forexample, at least after the application of the solid p-semiconductor bymeans of the process proposed, the low-oxygen atmosphere cannot beinterrupted again until after the encapsulation. Complete processing ofthe entire component in the low-oxygen atmosphere is also possible,without any adverse effect on the electrical properties of thecomponent. Particular preference is given to a low-oxygen atmosphere inthe form of an inert gas, for example a nitrogen atmosphere and/or anargon atmosphere. Mixed gases are also usable.

As detailed above, in a third aspect of the present invention, a processis proposed for producing a photovoltaic element. This may especially bea photovoltaic element according to one or more of the above-describedconfigurations, for example a dye solar cell. The proposed process forproducing the photovoltaic element may especially be performed using theabove-described process for producing a solid organic p-semiconductor,in which case the process for producing the solid organicp-semiconductor can be used once or more than once in the context of theproposed process for producing the photovoltaic element. Use of otherprocesses is, however, also possible in principle.

The process proposed preferably has the process steps describedhereinafter, which can preferably, but not necessarily, be performed inthe sequence described. Individual or several process steps can also beperformed overlapping in time and/or in parallel. In addition, theperformance of additional process steps which are not described ispossible. In the process proposed, at least one first electrode, atleast one n-semiconductive metal oxide, at least one dye which absorbselectromagnetic radiation, at least one solid organic p-semiconductorand at least one second electrode are provided. This provision can beeffected, for example, in the sequence mentioned. More particularly, theprovision can be effected by producing a layer structure, for exampleaccording to the above description. This layer structure can, forexample, be built up successively on one or more substrates. In thiscase, it is also possible to combine one or more of the elementsmentioned to give a combined layer, for example the n-semiconductivemetal oxide and the dye.

In the process proposed, the p-semiconductor is configured such that itcomprises silver in oxidized form, for example the at least onesilver(I) salt [Ag⁺]_(m)[A^(m−)] and especially preferably silverbis(trifluoromethylsulfonyl)imide. The p-semiconductor may especiallycomprise at least one organic matrix material which is doped by thesilver in oxidized form, for example the at least one silver(I) salt[Ag⁺]_(m)[A^(m−)] and especially preferably silverbis(trifluoromethylsulfonyl)imide. For possible configurations of theorganic matrix material and/or of the silver in oxidized form, forexample the at least one silver(I) salt [Ag⁺]_(m)[A^(m−)] and especiallypreferably silver bis(trifluoromethylsulfonyl)imide, reference may bemade to the description above and below.

The p-semiconductor can especially be produced by a process in which awet chemical processing operation is used, for example according to theabove description of the process for producing the solid organicp-semiconductor. In this wet chemical processing operation, at least onep-conductive organic matrix material and the silver in oxidized form,for example the at least one silver(I) salt [Ag⁺]_(m)[A^(m−)] andespecially preferably silver bis(trifluoromethylsulfonyl)imide, as ap-dopant can be applied together to at least one carrier element from atleast one liquid phase.

Hereinafter, further optionally implementable configurations of thephotovoltaic element and of the processes are described, which areparticularly preferred in the context of the invention. However, otherconfigurations are also possible in principle.

The photovoltaic element may especially comprise a layer structure,which may be applied, for example, to a substrate. In this case, forexample, the first electrode or the second electrode may face thesubstrate. At least one of the electrodes should be transparent. A“transparent” electrode in this context should especially be understoodto mean that, within the visible spectral range and/or in the range ofthe solar spectrum (approx. 300 nm to 2000 nm), transmission of at least50% exists, preferably of at least 80%. When the substrate is atransparent substrate, especially the electrode facing the substrateshould be transparent.

The substrate may be or comprise, for example, a glass substrate and/ora plastic substrate. However, other materials, including a combinationof different materials, are also usable in principle, for examplelaminates. The constituents of the photovoltaic element may be appliedto the substrate directly or indirectly as layers. In the context of thepresent invention, the terms “carrier element”, “carrier” and“substrate” are used at least substantially synonymously. When a carrierelement is being discussed, however, this if anything emphasizes thepossibility that a layer is being applied indirectly to the substrate,such that at least one further element, especially at least one furtherlayer, may be present between the layer to be applied and the actualsubstrate. However, direct application is also possible.

The photovoltaic element may especially be a dye solar cell.Accordingly, the photovoltaic element is also referred to hereinafter ingeneral terms as “cell”, without this imposing any restriction to aparticular layer structure. A cell may especially comprise the at leastone first electrode, the n-conductive metal oxide, the dye, thep-semiconductor and the second electrode. The n-conductive metal oxide,the dye and the p-semiconductor can also be referred to as functionallayers, which may be embedded between the electrodes. In addition, thecell may comprise one or more further layers which may, for example,likewise be assigned to the functional layers. One or more cells may beapplied directly or indirectly to a substrate. The photovoltaic elementmay especially comprise one cell or else a plurality of cells. Moreparticularly, a single-cell structure may be selected, or else amulticell structure, for example a tandem cell structure, with aplurality of cells arranged in parallel and/or one on top of another onthe substrate.

More particularly, the photovoltaic element according to the presentinvention may be configured in one or more of the ways which follow. Theconfigurations of the elements of the photovoltaic element can also becombined in virtually any way.

First Electrode and N-Semiconductive Metal Oxide

The n-semiconductive metal oxide used in the dye solar cell may be asingle metal oxide or a mixture of different oxides. It is also possibleto use mixed oxides. The n-semiconductive metal oxide may especially beporous and/or be used in the form of a nanoparticulate oxide,nanoparticles in this context being understood to mean particles whichhave an average particle size of less than 0.1 micrometer. Ananoparticulate oxide is typically applied to a conductive substrate(i.e. a carrier with a conductive layer as the first electrode) by asintering process as a thin porous film with large surface area.

The substrate may be rigid or else flexible. Suitable substrates (alsoreferred to hereinafter as carriers) are, as well as metal foils, inparticular plastic sheets or films and especially glass sheets or glassfilms. Particularly suitable electrode materials, especially for thefirst electrode according to the above-described, preferred structure,are conductive materials, for example transparent conductive oxides(TCOs), for example fluorine- and/or indium-doped tin oxide (FTO or ITO)and/or aluminum-doped zinc oxide (AZO), carbon nanotubes or metal films.Alternatively or additionally, it would, however, also be possible touse thin metal films which still have a sufficient transparency. Thesubstrate can be covered or coated with these conductive materials.Since generally only a single substrate is required in the structureproposed, the formation of flexible cells is also possible. This enablesa multitude of end uses which would be achievable only with difficulty,if at all, with rigid substrates, for example use in bank cards,garments, etc.

The first electrode, especially the TCO layer, may additionally becovered or coated with a solid metal oxide buffer layer (for example ofthickness 10 to 200 nm), in order to prevent direct contact of thep-semiconductor with the TCO layer (see Peng et al., Coord. Chem. Rev.248, 1479 (2004)). The inventive use of solid p-semiconductiveelectrolytes, in the case of which contact of the electrolyte with thefirst electrode is greatly reduced compared to liquid or gel-formelectrolytes, however, makes this buffer layer unnecessary in manycases, such that it is possible in many cases to dispense with thislayer, which also has a current-limiting effect and can also worsen thecontact of the n-semiconductive metal oxide with the first electrode.This enhances the efficiency of the components. On the other hand, sucha buffer layer can in turn be utilized in a controlled manner in orderto match the current component of the dye solar cell to the currentcomponent of the organic solar cell. In addition, in the case of cellsin which the buffer layer has been dispensed with, especially in solidcells, problems frequently occur with unwanted recombinations of chargecarriers. In this respect, buffer layers are advantageous in many casesspecifically in solid cells.

As is well known, thin layers or films of metal oxides are generallyinexpensive solid semiconductor materials (n-semiconductors), but theabsorption thereof, due to large bandgaps, is typically not within thevisible region of the electromagnetic spectrum, but rather usually inthe ultraviolet spectral region. For use in solar cells, the metaloxides therefore generally, as is the case in the dye solar cells, haveto be combined with a dye as a photosensitizer, which absorbs in thewavelength range of sunlight, i.e. at 300 to 2000 nm, and, in theelectronically excited state, injects electrons into the conduction bandof the semiconductor. With the aid of a solid p-semiconductor usedadditionally in the cell as an electrolyte, which is in turn reduced atthe counterelectrode (or, in the case of a tandem solar cell, at thetransition to the second subcell), electrons can be recycled to thesensitizer, such that it is regenerated.

Of particular interest for use in solar cells are the semiconductorszinc oxide, tin dioxide, titanium dioxide or mixtures of these metaloxides. The metal oxides can be used in the form of nanocrystallineporous layers. These layers have a large surface area which is coatedwith the dye as a sensitizer, such that a high absorption of sunlight isachieved. Metal oxide layers which are structured, for example nanorods,give advantages such as higher electron mobilities or improved porefilling by the dye.

The metal oxide semiconductors can be used alone or in the form ofmixtures. It is also possible to coat a metal oxide with one or moreother metal oxides. In addition, the metal oxides may also be applied asa coating to another semiconductor, for example GaP, ZnP or ZnS.

Particularly preferred semiconductors are zinc oxide and titaniumdioxide in the anatase polymorph, which is preferably used innanocrystalline form.

In addition, the sensitizers can advantageously be combined with alln-semiconductors which typically find use in these solar cells.Preferred examples include metal oxides used in ceramics, such astitanium dioxide, zinc oxide, tin(IV) oxide, tungsten(VI) oxide,tantalum(V) oxide, niobium(V) oxide, cesium oxide, strontium titanate,zinc stannate, complex oxides of the perovskite type, for example bariumtitanate, and binary and ternary iron oxides, which may also be presentin nanocrystalline or amorphous form.

Due to the strong absorption that customary organic dyes andphthalocyanines and porphyrins have, even thin layers or films of then-semiconductive metal oxide are sufficient to absorb the requiredamount of dye. Thin metal oxide films in turn have the advantage thatthe probability of unwanted recombination processes falls and that theinner resistance of the dye subcell is reduced. For the n-semiconductivemetal oxide, it is possible with preference to use layer thicknesses of100 nm up to 20 micrometers, more preferably in the range between 500 nmand approx. 3 micrometers.

Dye

In the context of the present invention, as usual for DSCs, the terms“dye”, “sensitizer dye” and “sensitizer” are used essentiallysynonymously without any restriction of possible configurations.Numerous dyes which are usable in the context of the present inventionare known from the prior art, and so, for possible material examples,reference may also be made to the above description of the prior artregarding dye solar cells. All dyes listed and claimed may in principlealso be present as pigments. Dye-sensitized solar cells based ontitanium dioxide as a semiconductor material are described, for example,in U.S. Pat. No. 4,927,721, Nature 353, p. 737-740 (1991) and U.S. Pat.No. 5,350,644, and also Nature 395, p. 583-585 (1998) and EP-A-1 176646. The dyes described in these documents can in principle also be usedadvantageously in the context of the present invention. These dye solarcells preferably comprise monomolecular films of transition metalcomplexes, especially ruthenium complexes, which are bonded to thetitanium dioxide layer via acid groups as sensitizers.

Not least for reasons of cost, sensitizers which have been proposedrepeatedly include metal-free organic dyes, which are likewise alsousable in the context of the present invention. High efficiencies ofmore than 4%, especially in solid dye solar cells, can be achieved, forexample, with indoline dyes (see, for example, Schmidt-Mende et al.,Adv. Mater. 2005, 17, 813). U.S. Pat. No. 6,359,211 describes the use,also implementable in the context of the present invention, of cyanine,oxazine, thiazine and acridine dyes which have carboxyl groups bondedvia an alkylene radical for fixing to the titanium dioxidesemiconductor.

Organic dyes now achieve efficiencies of almost 12.1% in liquid cells(see, for example, P. Wang et al., ACS. Nano 2010).Pyridinium-containing dyes have also been reported, can be used in thecontext of the present invention and exhibit promising efficiencies.

Particularly preferred sensitizer dyes in the dye solar cell proposedare the perylene derivatives, terrylene derivatives and quaterrylenederivatives described in DE 10 2005 053 995 A1 or WO 2007/054470 A1. Theuse of these dyes leads to photovoltaic elements with high efficienciesand simultaneously high stabilities.

The rylenes exhibit strong absorption in the wavelength range ofsunlight and can, depending on the length of the conjugated system,cover a range from about 400 nm (perylene derivatives I from DE 10 2005053 995 A1) up to about 900 nm (quaterrylene derivatives I from DE 102005 053 995 A1). Rylene derivatives I based on terrylene absorb,according to the composition thereof, in the solid state adsorbed ontotitanium dioxide, within a range from about 400 to 800 nm. In order toachieve very substantial utilization of the incident sunlight from thevisible into the near infrared region, it is advantageous to usemixtures of different rylene derivatives I. Occasionally, it may also beadvisable also to use different rylene homologs.

The rylene derivatives I can be fixed easily and in a permanent mannerto the n-semiconductive metal oxide film. The bonding is effected viathe anhydride function (×1) or the carboxyl groups —COOH or —COO— formedin situ, or via the acid groups A present in the imide or condensateradicals ((×2) or (×3)). The rylene derivatives I described in DE 102005 053 995 A1 have good suitability for use in dye-sensitized solarcells in the context of the present invention.

It is particularly preferred when the dyes, at one end of the molecule,have an anchor group which enables the fixing thereof to then-semiconductor film. At the other end of the molecule, the dyespreferably comprise electron donors Y which facilitate the regenerationof the dye after the electron has been released to the n-semiconductor,and also prevents recombination with electrons already released to thesemiconductor.

For further details regarding the possible selection of a suitable dye,it is possible, for example, again to refer to DE 10 2005 053 995 A1.For the tandem cells described in the present document, it is possibleespecially to use ruthenium complexes, porphyrins, other organicsensitizers, and preferably rylenes.

The dyes can be fixed onto or into the n-semiconductive metal oxidefilms in a simple manner. For example, the n-semiconductive metal oxidefilms can be contacted in the freshly sintered (still warm) state over asufficient period (for example about 0.5 to 24 h) with a solution orsuspension of the dye in a suitable organic solvent. This can beaccomplished, for example, by immersing the metal oxide-coated substrateinto the solution of the dye.

If combinations of different dyes are to be used, they may, for example,be applied successively from one or more solutions or suspensions whichcomprise one or more of the dyes. It is also possible to use two dyeswhich are separated by a layer of, for example, CuSCN (on this subjectsee, for example, Tennakone, K. J., Phys. Chem. B. 2003, 107, 13758).The most convenient method can be determined comparatively easily in theindividual case.

In the selection of the dye and of the size of the oxide particles ofthe n-semiconductive metal oxide, the solar cell should be configuredsuch that a maximum amount of light is absorbed. The oxide layers shouldbe structured such that the solid p-semiconductor can efficiently fillthe pores. For instance, smaller particles have greater surface areasand are therefore capable of adsorbing a greater amount of dyes. On theother hand, larger particles generally have larger pores which enablebetter penetration through the p-conductor.

As described above, the concept proposed comprises the use of one ormore solid p-semiconductors. In order to prevent recombination of theelectrons in the n-semiconductive metal oxide with the solidp-conductor, it is possible to use, between the n-semiconductive metaloxide and the p-semiconductor, at least one passivating layer which hasa passivating material. This layer should be very thin and should as faras possible cover only the as yet uncovered sites of then-semiconductive metal oxide. The passivation material may, under somecircumstances, also be applied to the metal oxide before the dye.Preferred passivation materials are especially one or more of thefollowing substances: Al₂O₃; silanes, for example CH₃SiCl₃; Al³⁺;4-tert-butylpyridine (TBP); MgO; GBA (4-guanidinobutyric acid) andsimilar derivatives; alkyl acids; hexadecylmalonic acid (HDMA).

P-Semiconductor

As described above, in the context of the photovoltaic element proposedhere, one or more solid organic p-semiconductors are used—alone or elsein combination with one or more further p-semiconductors which areorganic or inorganic in nature. The at least one solid organicp-semiconductor comprises, as described above, at least silver inoxidized form. In the context of the present invention, ap-semiconductor is generally understood to mean a material, especiallyan organic material, which is capable of conducting holes. Moreparticularly, it may be an organic material with an extensive π-electronsystem which can be oxidized stably at least once, for example to formwhat is called a free-radical cation. For example, the p-semiconductormay comprise at least one organic matrix material which has theproperties mentioned. More particularly, the p-semiconductor may bep-doped by the silver(I). This means that any p-semiconductive propertypresent in any case in the p-semiconductor or in the matrix material isenhanced or even actually created by the doping with silver(I). Moreparticularly, the doping can increase a charge carrier density,especially a hole density. Alternatively or additionally, a mobility ofthe charge carriers, especially of the holes, can also be influenced bythe doping, especially increased.

More particularly, the doped p-semiconductor, as described above, may beproducible or have been produced by applying at least one p-conductiveorganic material and silver in oxidized form to at least one carrierelement, wherein the silver in oxidized form is preferably applied to atleast one carrier element in the form of at least one silver(I) salt[Ag⁺]_(m)[A^(m−)] where A^(m−) is the anion of an organic or inorganicacid, and m is an integer in the range from 1 to 3, preferably where mis 1.

With regard to the integer m, m is preferably 1 or 2, very preferably 1.Accordingly, for production of the p-semiconductor, it is verypreferable to use a salt of the formula Ag⁺ A⁻.

With regard to A^(m−), this is preferably an anion of an organic orinorganic acid.

In a preferred embodiment, A^(m−) is an anion of an organic acid, theorganic acid preferably comprising at least one fluorine group or cyanogroup (—CN), more preferably at least one fluorine group. Preferably,[A^(m−)] is the anion of an organic carboxylic acid, sulfonic acid,phosphonic acid or sulfonimide each preferably comprising at least onefluorine group or cyano group.

Preferably, the present invention relates to a photovoltaic element, asdescribed above, where [A^(m−)] has a structure of the formula (II)

where R^(a) is a fluorine group —F or an alkyl radical, cycloalkylradical, aryl radical or heteroaryl radical each substituted by at leastone fluorine group or cyano group,and where X is —O⁻ or —N⁻—Rb,and where R^(b) comprises a fluorine group —F or a cyano group,and where R^(b) further comprises a group of the formula —S(O)₂—.

The term “cycloalkyl radical” or “cycloalkyl group” as used in thecontext of the present invention relates to cyclic, optionallysubstituted alkyl groups, preferably 5- or 6-membered rings ormulticyclic rings which further preferably have 5 to 20 carbon atoms.

R^(a) Radical:

In a preferred embodiment of the invention, R^(a) is —F or an alkylradical substituted at least by one fluorine group or one cyano group,preferably by at least one fluorine group, very preferably a methylgroup, ethyl group or propyl group substituted by at least one fluorinegroup or a cyano group, preferably a fluorine group. In addition to thefluorine group or the cyano group, the alkyl radical may comprise atleast one further substituent. Preferably, R^(a) comprises at least 3fluorine substituents or one cyano group, more preferably at least 3fluorine substituents.

R^(a) is especially selected from the group consisting of —F, —CF₃,—CF₂—CF₃ and —CH₂—CN, further preferably selected from the groupconsisting of —F, —CF₃ and —CF₂—CF₃.

Accordingly, the present invention also relates to a photovoltaicelement, as described above, where [A^(m−)] has a structure selectedfrom the following formulae:

and where X is —O⁻ or —N⁻—Rb. More preferably, R^(a) is —CF₃.

R^(b) Radical:

As described above, R^(b) is a group comprising a fluorine group —F or acyano group, where R^(b) additionally comprises a group of the formula—S(O)₂—. Preferably, R^(b) comprises at least one alkyl, cycloalkyl,aryl or heteroaryl radical, where the alkyl, cycloalkyl, aryl orheteroaryl radical is in each case substituted by at least one fluorinegroup —F or a cyano group, preferably by at least one fluorine group,and where R^(b) additionally comprises a group of the formula —S(O)₂—.

Preferably, R^(b) has a structure of the following formula:

where R^(bb) is —F or an alkyl group substituted by at least onefluorine group or a cyano group, preferably at least one fluorine group,very preferably a methyl group, ethyl group or propyl group substitutedby at least one fluorine group. In addition to the fluorine group and/orcyano group, the alkyl radical may comprise at least one furthersubstituent. Preferably, R^(bb) comprises at least 3 fluorinesubstituents.

R^(bb) is especially selected from the group consisting of —F, —CF₃,—CF₂—CF₃ and —S(O)₂—CH₂—CN, especially selected from the groupconsisting of —F, —CF₃ and —CF₂—CF₃.

Accordingly, the present invention also relates to a photovoltaicelement as described above, where X is —N⁻—R^(b), and where R^(b) isselected from the group consisting of —S(O)₂—F, —S(O)₂—CF₃,—S(O)₂—CF₂—CF₃ and —S(O)₂—CH₂—CN, especially selected from the groupconsisting of —S(O)₂—F, —S(O)₂—CF₃, and —S(O)₂—CF₂—CF₃.

[A^(m−)] accordingly most preferably has one of the followingstructures:

where R^(a) is especially selected from the group consisting of —F, —CF₃and —CF₂—CF₃. Preferably, in the case that X is —N⁻—Rb and Rb has thestructure

R^(a) and R^(bb) are the same; [A^(m−)] is accordingly more preferably asymmetric sulfonylimide. In a preferred embodiment, [A^(m−)] isaccordingly selected from bis(trifluoromethylsulfonyl)imide (TFSI⁻),bis(trifluoroethylsulfonyl)imide, and bis(fluorosulfonyl)imide.

In an alternative embodiment, the present invention relates to aphotovoltaic element as described above where [A^(m−)] is atrifluoroacetate group.

In a further preferred embodiment, [A^(m−)] is the anion of an inorganicacid. In this case, [A^(m−)] is preferably —NO₃ ⁻ (nitrate).Accordingly, the present invention also relates to a photovoltaicelement which, as described above, is producible or has been produced byintroducing, especially mixing and/or dissolving, at least one silver(I)salt [Ag⁺]_(m)[A^(m−)] into at least one organic matrix material (128),where [A^(m−)] is an —NO₃ ⁻ group and where m=1.

Accordingly, the present invention also relates to a photovoltaicelement as described above, where [A^(m−)] is selected from the groupconsisting of bis(trifluoromethylsulfonyl)imide (TFSI⁻),bis(trifluoroethylsulfonyl)imide, bis(fluorosulfonyl)imide,trifluoromethylsulfonate, preferably where [A^(m−)] isbis(trifluoromethylsulfonyl)imide (TFSI⁻).

Solid p-semiconductors doped with at least silver in oxidized form, forexample the at least one silver(I) salt [Ag⁺]_(m)[A^(m−)] and especiallypreferably silver bis(trifluoromethylsulfonyl)imide, can be used in theinventive photovoltaic elements even without any great increase in thecell resistance, especially when the dyes absorb strongly and thereforerequire only thin n-semiconductor layers. More particularly, thep-semiconductor should essentially have a continuous, impervious layer,in order that unwanted recombination reactions which could result fromcontact between the n-semiconductive metal oxide (especially innanoporous form) with the second electrode and/or further elements ofthe photovoltaic element are reduced.

The silver in oxidized form, for example the at least one silver(I) salt[Ag⁺]_(m)[A^(m−)] and especially preferably silverbis(trifluoromethylsulfonyl)imide, can especially be applied to thecarrier element, together with the matrix material from the liquidphase. For example, the silver in oxidized form, for example the atleast one silver(I) salt [Ag⁺]_(m)[A^(m−)] and especially preferablysilver bis(trifluoromethylsulfonyl)imide, can be processed as asolution, dispersion or suspension, in combination with ap-semiconductive matrix material. Optionally, at least one organic saltcan be added to this at least one liquid phase (though it is alsopossible for several liquid phases to be present), for example forstabilization purposes and/or for improvement of the electricalproperties.

A significant parameter influencing the selection of the p-semiconductoris the hole mobility, since this partly determines the hole diffusionlength (cf. Kumara, G., Langmuir, 2002, 18, 10493-10495). A comparisonof charge carrier mobilities in different spiro compounds can be found,for example, in T. Saragi, Adv. Funct. Mater. 2006, 16, 966-974.

Preferably, in the context of the present invention, organicsemiconductors are used (i.e. low molecular weight, oligomeric orpolymeric semiconductors or mixtures of such semiconductors). Particularpreference is given to p-semiconductors which can be processed from aliquid phase. Examples here are p-semiconductors based on polymers suchas polythiophene and polyarylamines, or on amorphous, reversiblyoxidizable, nonpolymeric organic compounds, such as the spirobifluorenesmentioned at the outset (cf., for example, US 2006/0049397 and the spirocompounds disclosed therein as p-semiconductors, which are also usablein the context of the present invention). Preference is given to usinglow molecular weight organic semiconductors. The solid p-semiconductorscan be used in doped form with silver in oxidized form, for example theat least one silver(I) salt [Ag⁺]_(m)[A^(m−)] and especially preferablysilver bis(trifluoromethyl-sulfonyl)imide, as a dopant.

In addition, reference may also be made to the remarks regarding thep-semiconductive materials and dopants from the description of the priorart. For the other possible elements and the possible structure of thedye solar cell, reference may also be made substantially to the abovedescription.

Second Electrode

The second electrode may be a bottom electrode facing the substrate orelse a top electrode facing away from the substrate. The secondelectrodes which can be used are especially metal electrodes which mayhave one or more metals in pure form or as a mixture/alloy, such asespecially aluminum or silver. The use of inorganic/organic mixedelectrodes or multilayer electrodes is also possible, for example theuse of LiF/Al electrodes.

In addition, it is also possible to use electrode designs in which thequantum efficiency of the components is increased by virtue of thephotons being forced, by means of appropriate reflections, to passthrough the absorbing layers at least twice.

Such layer structures are also referred to as “concentrators” and arelikewise described, for example, in WO 02/101838 (especially p. 23-24).

BRIEF DESCRIPTION OF THE FIGURES

Further details and features of the invention are evident from thedescription of preferred embodiments which follows in conjunction withthe dependent claims. In this context, the particular features may beimplemented alone or with several in combination. The invention is notrestricted to the working examples. The working examples are shownschematically in the figures. Identical reference numerals in theindividual figures refer to identical elements or elements withidentical function, or elements which correspond to one another withregard to their functions.

The individual figures show:

FIG. 1 a schematic layer structure of an inventive organic photovoltaicelement in a sectional diagram in side view;

FIG. 2 a schematic arrangement of the energy levels in the layerstructure according to FIG. 1;

FIG. 3 current-voltage characteristic of a comparative sample withoutsilver in oxidized form, measured 2 days after production;

FIG. 4 current-voltage characteristics with Ag-TFSI doping.

WORKING EXAMPLES

FIG. 1 shows, in a highly schematic sectional diagram, a photovoltaicelement 110 which, in this working example, is a dye solar cell 112. Thephotovoltaic element 110 according to the schematic layer structure inFIG. 1 can be configured in accordance with the invention. Thecomparative sample according to the prior art may in principle alsocorrespond to the structure shown in FIG. 1, and differ therefrom, forexample, merely with regard to the solid organic p-semiconductor. It ispointed out that the present invention, however, is also usable in otherlayer structures and/or in other constructions.

The photovoltaic element 110 comprises a substrate 114, for example aglass substrate. Other substrates are also usable, as described above.Applied to this substrate 114 is a first electrode 116, which is alsoreferred to as a working electrode and which preferably, as describedabove, is transparent. Applied to this first electrode 116 in turn is ablocking layer 118 of an optional metal oxide, which is preferablynonporous and/or nonparticulate. Applied to this in turn is ann-semiconductive metal oxide 120 which has been sensitized with a dye122.

The substrate 114 and the layers 116 to 120 applied thereto form acarrier element 124 for at least one layer, applied thereto, of a solidorganic p-semiconductor 126, which in turn may comprise especially atleast one p-semiconductive organic matrix material 128 and at least onesilver in oxidized form 130, for example the at least one silver(I) salt[Ag⁺]_(m)[A^(m−)] and especially preferably silverbis(trifluoromethylsulfonyl)imide. Applied to this p-semiconductor 126is a second electrode 132, which is also referred to as thecounterelectrode. The layers shown in FIG. 1 together form a layerstructure 134 which has been shielded from a surrounding atmosphere byan encapsulation 136, for example in order to completely or partiallyprotect the layer structure 134 from oxygen and/or moisture. One or bothof the electrodes 116, 132 may, as indicated in FIG. 1 with reference tothe first electrode 116, be conducted out of the encapsulation 136, inorder to be able to provide one or more contact connection areas outsidethe encapsulation 136.

FIG. 2 shows, by way of example, in a highly schematic manner, an energylevel diagram of the photovoltaic element 110, for example according toFIG. 1. What are shown are the Fermi levels 138 of the first electrode116 and of the second electrode 132, and the HOMOs (highest occupiedmolecular orbitals) 140 and the LUMOs (lowest unoccupied molecularorbitals) of the layers 118/120 (which may comprise the same material,for example TiO₂) of the dye (shown by way of example with a HOMO levelof 5.7 eV) and of the p-semiconductor 126 (also referred to as HTL, holetransport layer). The materials specified by way of example for thefirst electrode 116 and the second electrode 132 are FTO (fluorine-dopedtin oxide) and silver.

The photovoltaic elements may additionally optionally comprise furtherelements. By means of photovoltaic elements 110 with or withoutencapsulation 136, the working examples described hereinafter wereimplemented, on the basis of which the effect of the present inventionand especially of the p-doping of the p-semiconductor 126 by means ofsilver in oxidized form 130 can be demonstrated.

Comparative Sample

As a comparative sample of a photovoltaic element, a dye solar cell witha solid p-semiconductor without doping with silver in oxidized form wasproduced, as known in principle from the prior art.

As the base material and substrate, glass plates which had been coatedwith fluorine-doped tin oxide (FTO) as the first electrode (workingelectrode) and were of dimensions 25 mm×25 mm×3 mm (Hartford Glass) wereused, which were treated successively in an ultrasound bath with glasscleaner (RBS 35), demineralized water and acetone, for 5 min in eachcase, then boiled in isopropanol for 10 min and dried in a nitrogenstream.

To produce an optional solid TiO₂ buffer layer, a spray pyrolysisprocess was used. Thereon, as an n-semiconductive metal oxide, a TiO₂paste (Dyesol) which comprises TiO₂ particles with a diameter of 25 nmin a terpineol/ethylcellulose dispersion was spun on with a spin-coaterat 4500 rpm and dried at 90° C. for 30 min. After heating to 450° C. for45 min and a sintering step at 450° C. for 30 minutes, a TiO₂ layerthickness of approximately 1.8 μm was obtained.

After removal from the drying cabinet, the sample was cooled to 80° C.and immersed into a 5 mM solution of an additive ID662 (obtainableaccording to example H, for example) for 12 h and subsequently into a0.5 mM solution of a dye in dichloromethane for 1 h.

The dye used was the dye ID504 (obtainable according to example G, forexample). After removal from the solution, the sample was subsequentlyrinsed with the same solvent and dried in a nitrogen stream. The samplesobtained in this way were subsequently dried at 40° C. under reducedpressure.

Next, a p-semiconductor solution was spun on. For this purpose, asolution of 0.12 M spiro-MeOTAD (Merck) and 20 mM LiN(SO₂CF₃)₂ (Aldrich)in chlorobenzene was made up. 125 μl of this solution were applied tothe sample and allowed to act for 60 s. Thereafter, the supernatantsolution was spun off at 2000 rpm for 30 s and the sample was storedunder air in the dark overnight. As stated above, it is suspected thatthis storage brings about oxygen doping of the p-semiconductor, as aresult of which the conductivity of the p-semiconductor is enhanced.

Finally, a metal back electrode was applied as a second electrode bythermal metal vaporization under reduced pressure. The metal used wasAg, which was vaporized at a rate of 3 Å/s at a pressure of approx.2*10⁻⁶ mbar, so as to give a layer thickness of about 200 nm.

After the production, the cell was stored under dry air (8% relative airhumidity) for 2 days.

To determine the efficiency T₁, the particular current/voltagecharacteristic was measured with a source meter model 2400 (KeithleyInstruments Inc.) under irradiation with a xenon solar simulator(LOT-Oriel 300 W AM 1.5) two days after production. The initialmeasurement was effected with unencapsulated cells. A current-voltagecharacteristic of the comparative sample measured after two days isshown in FIG. 3. The comparative sample had the characteristics shown intable 1.

TABLE 1 Characteristics of comparative sample without doping.Isc[mA/cm²] Voc[mV] FF[%] ETA[%] no Ag-TFSI, t = 2 days 9.29 860 55 4.4

The short-circuit current Isc (i.e. the current density at loadresistance zero) was 9.29 mA/cm², the open-circuit voltage V_(oc) (i.e.the load at which the current density has fallen to zero) was 860 mV,the fill factor FF was 55% and the efficiency ETA was 4%.

Example 1 Doping with 5 mm AG-TFSI

As the first working example of an inventive photovoltaic element 110,the above-described comparative sample was modified by doping thep-semiconductor 126 or the matrix material 128 thereof with silverbis(trifluoromethylsulfonyl)imide (Ag-TFSI). For this purpose, 5 mmsilver bis(trifluoromethylsulfonyl)imide (source: Aldrich) incyclohexanone was added to the p-semiconductor solution of 0.12Mspiro-MeOTAD (source: Merck) and 20 mm LiN(BO₂CF₃)₂ (source: Aldrich) inchlorobenzene. This solution was then spun onto the sample as describedfor the comparative sample.

The metal back electrode as the second electrode 132 was appliedimmediately thereafter by thermal metal vaporization under reducedpressure. The metal used was Ag, which was vaporized at a rate of 3 Å/sat a pressure of approx. 2*10⁻⁶ mbar so as to form a layer thickness ofabout 200 nm.

To determine the efficiency η, the particular current/voltagecharacteristic was measured with a Source Meter Model 2400 (KeithleyInstruments Inc.) under irradiation with a xenon solar simulator(LOT-Oriel 300 W AM 1.5) immediately and 2 days after production. Theinitial measurement was effected with unencapsulated cells.

Current-voltage characteristics with 5 mm silverbis(trifluoromethylsulfonyl)imide are shown in FIG. 4. Thecharacteristics of the comparative sample and of the sample according toexample 1 are shown in table 2.

TABLE 2 Comparison of characteristics of an undoped comparative sampleand of a sample according to example 1 at different measurement times.Isc[mA/cm²] Voc[mV] FF[%] ETA[%] no Ag-TFSI, t = 0 4.13 760 26 0.8 noAg-TFSI, t = 2 days 9.29 860 55 4.4 with Ag-TFSI, t = 0 9.20 800 69 5.1with Ag-TFSI, t = 2 days 9.80 780 66 5.0

Example 2 Variation of the Dopant Concentration

In order to study the influence of the amount of dopant on theproperties of the photovoltaic element 110, variations of example 1 wereadditionally produced with 1-20 mm silverbis(trifluoromethylsulfonyl)imide. Otherwise, the samples were producedlike the sample according to the above-described example 1. Thecharacteristics of these samples, measured after 2 days, are shown intable 3. The illumination in these measurements was in each case again100 sun, as already in the measurements above.

TABLE 3 Comparison of characteristics of samples according to example 2with different Ag-TFSI content. Isc[mA/cm²] Voc[mV] FF[%] ETA[%]  1 mMAg-TFSI −10.4 780 53 4.3  3 mM Ag-TFSI −10.1 780 62 4.8  5 mM Ag-TFSI−9.8 780 66 5.0 10 mM Ag-TFSI −9.7 760 69 5.1 20 mM Ag-TFSI −9.7 800 644.9

The measurements show that, in terms of efficiency, a maximum of approx.5.1% occurs at approx. 10 mm Ag-TFSI. Overall, the efficiency between 3mm and 20 mm, however, follows a comparatively flat profile, which mayconstitute an advantage in terms of production technology.

Example 3 Variation of the Matrix Material

In addition, as example 3, the influence of the matrix material 128 onthe properties of the photovoltaic elements 110 was studied. For thispurpose, samples were produced according to the above-described example1, except that spiro-MeOTAD as matrix material 128 was replaced bydifferent matrix materials 128 with different concentrations, moreparticularly by the matrix materials of the ID522, ID322 and ID367 typesalready mentioned above. To introduce silver 130 in oxidized form, thedopant used was again in each case 10 mm silverbis(trifluoromethylsulfonyl)imide in all samples. The characteristics ofthe samples obtained in this way are shown in table 4. The specifiedconcentrations of 160 mg/ml and 200 mg/ml are based on the concentrationof the matrix material 128 in the liquid phase. The characteristics wereagain recorded after 2 days and measured at 100 sun [mW/cm²].

TABLE 4 Comparison of characteristics of samples according to example 4with different matrix materials. Isc Voc p-Conductor Comment [mA/cm²][mV] FF[%] ETA[%] ID522 conc. 160 mg/ml, −6.22 740 73 3.4 10 mM AgTFSIID522 conc. 200 mg/ml, −7.07 740 70 3.7 10 mMAgTFSI ID322 conc. 160mg/ml, −1.68 500 40 0.3 10 mM AgTFSI ID322 conc. 200 mg/ml, −1.49 580 390.3 10 mMAgTFSI ID367 conc. 160 mg/ml, −6.89 760 73 3.8 10 mM AgTFSIID367 conc. 200 mg/ml, −7.14 740 71 3.7 10 mMAgTFSI

Example 4 Variation of the Dopant

In addition, tests in which silver 130 in oxidized form was introducedinto the matrix material 128 by means of other dopants were conducted.In addition, silver in Ag-TFSI was replaced by other groups in order tocheck whether the doping effect and the positive effect thereof on thecharacteristics of the photovoltaic components 110 is possibly caused byTFSI instead of by the silver 130 in oxidized form.

For this purpose, in example 4, various samples which correspond againto example 1 above apart from the dopant were produced. Instead ofAg-TFSI, however, other salts as dopants were each added in an amount of20 mm. The results are shown in table 5. Silver nitrate was added insolid form to the p-conductor solution.

TABLE 5 Comparison of characteristics of samples according to example 5with different dopants. Dopant Isc[mA/cm²] Voc[mV] FF[%] ETA[%] Agnitrate −9.8 800 66 5.1 Ag triflate −4.4 920 43 1.8 Ag trifluoroacetate−1.2 640 35 0.3 1-ethyl-3-methyl-TFSI −1.9 1000 39 0.71-butyl-3-methyl-TFSI −1.2 1000 26 0.3 Na triflate −1.6 1000 29 0.5

The results show that TFSI in general leads to high efficiencies only asan anion in a silver salt. In addition to Ag-TFSI, however, other silversalts also exhibit comparatively high efficiencies, especially silvernitrate and silver triflate. In general, it is thus possible to usecompounds, especially salts, containing silver in oxidized form as adopant, especially silver(I) salts of the formula [Ag⁺]_(m)[A^(m−)],more preferably Ag-TFSI, silver nitrate and silver triflate.

Finally, synthesis examples of low molecular weight organicp-semiconductors are also listed hereinafter, which are usableindividually or in combination in the context of the present inventionand which can, for example, satisfy the formula I given above.

Synthesis Examples (A) General Synthesis Schemes for Preparation ofCompounds of the Formula I (a) Synthesis Route is

(a1) Synthesis Step I-R1:

The synthesis in synthesis step I-R1 was based on the references citedbelow:

-   a) Liu, Yunqi; Ma, Hong; Jen, Alex K-Y.; CHCOFS; Chem. Commun.; 24;    1998; 2747-2748,-   b) Goodson, Felix E.; Hauck, Sheila; Hartwig, John F.; J. Am. Chem.    Soc.; 121; 33; 1999; 7527-7539,-   c) Shen, Jiun Yi; Lee, Chung Ying; Huang, Tai-Hsiang; Lin, Jiann T.;    Tao, Yu-Tai; Chien, Chin-Hsiung; Tsai, Chiitang; J. Mater. Chem.;    15; 25; 2005; 2455-2463,-   d) Huang, Ping-Hsin; Shen, Jiun-Yi; Pu, Shin-Chien; Wen, Yuh-Sheng;    Lin, Jiann T.; Chou, Pi-Tai; Yeh, Ming-Chang P.; J. Mater. Chem.;    16; 9; 2006; 850-857,-   e) Hirata, Narukuni; Kroeze, Jessica E.; Park, Taiho; Jones, David;    Haque, Saif A.; Holmes, Andrew B.; Durrant, James R.; Chem. Commun.;    5; 2006; 535-537.    (a2) Synthesis Step I-R2:

The synthesis in synthesis step I-R2 was based on the references citedbelow:

-   a) Huang, Qinglan; Evmenenko, Guennadi; Dutta, Pulak; Marks, Tobin    J.; J. Am. Chem. Soc.; 125; 48; 2003; 14704-14705,-   b) Bacher, Erwin; Bayerl, Michael; Rudati, Paula; Reckefuss, Nina;    Mueller, C. David; Meerholz, Klaus; Nuyken, Oskar; Macromolecules;    EN; 38; 5; 2005; 1640-1647,-   c) Li, Zhong Hui; Wong, Man Shing; Tao, Ye; D'Iorio, Marie; J. Org.    Chem.; EN; 69; 3; 2004; 921-927.    (a3) Synthesis Step I-R3:

The synthesis in synthesis step I-R3 was based on the reference citedbelow:

-   J. Grazulevicius; J. of Photochem. and Photobio., A: Chemistry 2004    162(2-3), 249-252.

The compounds of the formula I can be prepared via the sequence ofsynthesis steps shown above in synthesis route I. In steps (I-R1) to(I-R3), the reactants can be coupled, for example, by Ullmann reactionwith copper as a catalyst or under palladium catalysis.

(b) Synthesis Route II:

(b1) Synthesis Step II-R1:

The synthesis in synthesis step II-R1 was based on the references citedunder I-R2.

(b2) Synthesis Step II-R2:

The synthesis in synthesis step II-R2 was based on the references citedbelow:

-   a) Bacher, Erwin; Bayerl, Michael; Rudati, Paula; Reckefuss, Nina;    Müller, C. David; Meerholz, Klaus; Nuyken, Oskar; Macromolecules;    38; 5; 2005; 1640-1647,-   b) Goodson, Felix E.; Hauck, Sheila; Hartwig, John F.; J. Am. Chem.    Soc.; 121; 33; 1999; 7527-7539; Hauck, Sheila I.; Lakshmi, K. V.;    Hartwig, John F.; Org. Lett.; 1; 13; 1999; 2057-2060.    (b3) Synthesis Step II-R3:

The compounds of the formula I can be prepared via the sequence ofsynthesis steps shown above in synthesis route II. In steps (II-R1) to(II-R3), the reactants can be coupled, as also in synthesis route I, forexample, by Ullmann reaction with copper as a catalyst or underpalladium catalysis.

(c) Preparation of the Starting Amines:

When the diarylamines in synthesis steps I-R2 and II-R1 of synthesisroutes I and II are not commercially available, they can be prepared,for example, by Ullmann reaction with copper as a catalyst or underpalladium catalysis, according to the following reaction:

The synthesis was based on the review articles listed below:

Palladium-catalyzed C—N coupling reactions:

-   a) Yang, Buchwald; J. Organomet. Chem. 1999, 576 (1-2), 125-146,-   b) Wolfe, Marcoux, Buchwald; Acc. Chem. Res. 1998, 31, 805-818,-   c) Hartwig; Angew. Chem. Int. Ed. Engl. 1998, 37, 2046-2067.

Copper-catalyzed C—N coupling reactions:

-   a) Goodbrand, Hu; Org. Chem. 1999, 64, 670-674,-   b) Lindley; Tetrahedron 1984, 40, 1433-1456.

(B) Synthesis example 1 Synthesis of the Compound ID367 (Synthesis RouteI) (B1): Synthesis Step According to General Synthesis Scheme I-R1

A mixture of 4,4′-dibromobiphenyl (93.6 g; 300 mmol), 4-methoxyaniline(133 g; 1.08 mol), Pd(dppf)Cl₂(Pd(1,1-bis(diphenylphosphino)ferrocene)Cl₂; 21.93 g; 30 mmol) andt-BuONa (sodium tert-butoxide; 109.06 g; 1.136 mol) in toluene (1500 ml)was stirred under a nitrogen atmosphere at 110° C. for 24 hours. Aftercooling, the mixture was diluted with diethyl ether and filtered througha Celite® pad (from Carl Roth). The filter bed was washed with 1500 mleach of ethyl acetate, methanol and methylene chloride. The product wasobtained as a light brown solid (36 g; yield: 30%).

¹H NMR (400 MHz, DMSO): δ 7.81 (s, 2H), 7.34-7.32 (m, 4H), 6.99-6.97 (m,4H), 6.90-6.88 (m, 4H), 6.81-6.79 (m, 4H), 3.64 (s, 6H).

(B2): Synthesis Step According to General Synthesis Scheme I-R2

Nitrogen was passed for a period of 10 minutes through a solution ofdppf (1,1′-bis(diphenyl-phosphino)ferrocene; 0.19 g; 0.34 mmol) andPd₂(dba)₃ (tris(dibenzylideneacetone)-dipalladium(0); 0.15 g; 0.17 mmol)in toluene (220 ml). Subsequently, t-BuONa (2.8 g; 29 mmol) was addedand the reaction mixture was stirred for a further 15 minutes.4,4′-Dibromobiphenyl (25 g; 80 mmol) and 4,4′-dimethoxydiphenylamine(5.52 g; 20 mmol) were then added successively. The reaction mixture washeated at a temperature of 100° C. under a nitrogen atmosphere for 7hours. After cooling to room temperature, the reaction mixture wasquenched with ice-water, and the precipitated solid was filtered off anddissolved in ethyl acetate. The organic layer was washed with water,dried over sodium sulfate and purified by column chromatography (eluent:5% ethyl acetate/hexane). A pale yellow solid was obtained (7.58 g,yield: 82%).

¹H NMR (300 MHz, DMSO-d₆): 7.60-7.49 (m, 6H), 7.07-7.04 (m, 4H),6.94-6.91 (m, 4H), 6.83-6.80 (d, 2H), 3.75 (s, 6H).

(B3). Synthesis Step According to General Synthesis Scheme I-R3

N⁴,N⁴′-Bis(4-methoxyphenyl)biphenyl-4,4′-diamine (product from synthesisstep I-R1; 0.4 g; 1.0 mmol) and product from synthesis step I-R2 (1.0 g;2.2 mmol) were added under a nitrogen atmosphere to a solution oft-BuONa (0.32 g; 3.3 mmol) in o-xylene (25 ml). Subsequently, palladiumacetate (0.03 g; 0.14 mmol) and a solution of 10% by weight of P(t-Bu)₃(tris-t-butylphosphine) in hexane (0.3 ml; 0.1 mmol) were added to thereaction mixture which was stirred at 125° C. for 7 hours. Thereafter,the reaction mixture was diluted with 150 ml of toluene and filteredthrough Celite®, and the organic layer was dried over Na₂SO₄. Thesolvent was removed and the crude product was reprecipitated three timesfrom a mixture of tetrahydrofuran (THF)/methanol. The solid was purifiedby column chromatography (eluent: 20% ethyl acetate/hexane), followed bya precipitation with THF/methanol and an activated carbon purification.After removing the solvent, the product was obtained as a pale yellowsolid (1.0 g, yield: 86%).

¹H NMR (400 MHz, DMSO-d₆): 7.52-7.40 (m, 8H), 6.88-7.10 (m, 32H),6.79-6.81 (d, 4H), 3.75 (s, 6H), 3.73 (s, 12H).

(C) Synthesis Example 2 Synthesis of the Compound ID447 (Synthesis RouteII) (C1) Synthesis Step According to General Synthesis Scheme II-R2

p-Anisidine (5.7 g, 46.1 mmol), t-BuONa (5.5 g, 57.7 mol) and P(t-Bu)₃(0.62 ml, 0.31 mmol) were added to a solution of the product fromsynthesis step I-R2 (17.7 g, 38.4 mmol) in toluene (150 ml). Afternitrogen had been passed through the reaction mixture for 20 minutes,Pd₂(dba)₃ (0.35 g, 0.38 mmol) was added. The resulting reaction mixturewas left to stir under a nitrogen atmosphere at room temperature for 16hours. Subsequently, it was diluted with ethyl acetate and filteredthrough Celite®. The filtrate was washed twice with 150 ml each of waterand saturated sodium chloride solution. After the organic phase had beendried over Na₂SO₄ and the solvent had been removed, a black solid wasobtained. This solid was purified by column chromatography (eluent:0-25% ethyl acetate/hexane). This afforded an orange solid (14 g, yield:75%).

¹H NMR (300 MHz, DMSO): 7.91 (s, 1H), 7.43-7.40 (d, 4H), 7.08-6.81 (m,16H), 3.74 (s, 6H), 3.72 (s, 3H).

(C2) Synthesis Step According to General Synthesis Scheme II-R3

t-BuONa (686 mg; 7.14 mmol) was heated at 100° C. under reducedpressure, then the reaction flask was purged with nitrogen and allowedto cool to room temperature. 2,7-Dibromo-9,9-dimethylfluorene (420 mg;1.19 mmol), toluene (40 ml) and Pd[P(^(t)Bu)₃]₂ (20 mg; 0.0714 mmol)were then added, and the reaction mixture was stirred at roomtemperature for 15 minutes. Subsequently,N,N,N′-p-trimethoxytriphenylbenzidine (1.5 g; 1.27 mmol) was added tothe reaction mixture which was stirred at 120° C. for 5 hours. Themixture was filtered through a Celite®/MgSO₄ mixture and washed withtoluene. The crude product was purified twice by column chromatography(eluent: 30% ethyl acetate/hexane) and, after twice reprecipitating fromTHF/methanol, a pale yellow solid was obtained (200 mg, yield: 13%).

¹H NMR: (400 MHz, DMSO-d₆): 7.60-7.37 (m, 8H), 7.02-6.99 (m, 16H),6.92-6.87 (m, 20H), 6.80-6.77 (d, 2H), 3.73 (s, 6H), 3.71 (s, 12H), 1.25(s, 6H)

(D) Synthesis Example 3 Synthesis of the Compound ID453 (Synthesis RouteI) (D1) Preparation of the Starting Amine Step 1:

NaOH (78 g; 4 eq) was added to a mixture of 2-bromo-9H-fluorene (120 g;1 eq) and BnEt₃NCl (benzyltriethylammonium chloride; 5.9 g; 0.06 eq) in580 ml of DMSO (dimethyl sulfoxide). The mixture was cooled withice-water, and methyl iodide (MeI) (160 g; 2.3 eq) was slowly addeddropwise. The reaction mixture was left to stir overnight, then pouredinto water and subsequently extracted three times with ethyl acetate.The combined organic phases were washed with a saturated sodium chloridesolution and dried over Na₂SO₄, and the solvent was removed. The crudeproduct was purified by column chromatography using silica gel (eluent:petroleum ether). After washing with methanol, the product(2-bromo-9,9′-dimethyl-9H-fluorene) was obtained as a white solid (102g).

¹H NMR (400 MHz, CDCl3): δ 1.46 (s, 6H), 7.32 (m, 2H), 7.43 (m, 2H),7.55 (m, 2H), 7.68 (m, 1H)

Step 2:

p-Anisidine (1.23 g; 10.0 mmol) and 2-bromo-9,9′-dimethyl-9H-fluorene(3.0 g; 11.0 mmol) were added under a nitrogen atmosphere to a solutionof t-BuONa (1.44 g; 15.0 mmol) in 15 ml of toluene (15 ml). Pd₂(dba)₃(92 mg; 0.1 mmol) and a 10% by weight solution of P(t-Bu)₃ in hexane(0.24 ml; 0.08 mmol) were added, and the reaction mixture was stirred atroom temperature for 5 hours. Subsequently, the mixture was quenchedwith ice-water, and the precipitated solid was filtered off anddissolved in ethyl acetate. The organic phase was washed with water anddried over Na₂SO₄. After purifying the crude product by columnchromatography (eluent: 10% ethyl acetate/hexane), a pale yellow solidwas obtained (1.5 g, yield: 48%).

¹H NMR (300 MHz, C₆D₆): 7.59-7.55 (d, 1H), 7.53-7.50 (d, 1H), 7.27-7.22(t, 2H), 7.19 (s, 1H), 6.99-6.95 (d, 2H), 6.84-6.77 (m, 4H), 4.99 (s,1H), 3.35 (s, 3H), 1.37 (s, 6H).

(D2) Preparation of the Compound ID453 for Use in Accordance with theInvention (D2.1): Synthesis Step According to General Synthesis SchemeI-R2:

Product from a) (4.70 g; 10.0 mmol) and 4,4′-dibromobiphenyl (7.8 g; 25mmol) were added to a solution of t-BuONa (1.15 g; 12 mmol) in 50 ml oftoluene under nitrogen. Pd₂(dba)₃ (0.64 g; 0.7 mmol) and DPPF (0.78 g;1.4 mmol) were added, and the reaction mixture was left to stir at 100°C. for 7 hours. After the reaction mixture had been quenched withice-water, the precipitated solid was filtered off and it was dissolvedin ethyl acetate. The organic phase was washed with water and dried overNa₂SO₄. After purifying the crude product by column chromatography(eluent: 1% ethyl acetate/hexane), a pale yellow solid was obtained (4.5g, yield: 82%).

¹H NMR (400 MHz, DMSO-d6): 7.70-7.72 (d, 2H), 7.54-7.58 (m, 6H),7.47-7.48 (d, 1H), 7.21-7.32 (m, 3H), 7.09-7.12 (m, 2H), 6.94-6.99 (m,4H), 3.76 (s, 3H), 1.36 (s, 6H).

(D2.2) Synthesis Step According to General Synthesis Scheme I-R3:

N⁴,N⁴′-Bis(4-methoxyphenyl)biphenyl-4,4′-diamine (0.60 g; 1.5 mmol) andproduct from the preceding synthesis step I-R2 (1.89 g; 3.5 mmol) wereadded under nitrogen to a solution of t-BuONa (0.48 g; 5.0 mmol) in 30ml of o-xylene. Palladium acetate (0.04 g; 0.18 mmol) and P(t-Bu)₃ in a10% by weight solution in hexane (0.62 ml; 0.21 mmol) were added, andthe reaction mixture was stirred at 125° C. for 6 hours. Subsequently,the mixture was diluted with 100 ml of toluene and filtered throughCelite®. The organic phase was dried over Na₂SO₄ and the resulting solidwas purified by column chromatography (eluent: 10% ethylacetate/hexane). This was followed by reprecipitation from THF/methanolto obtain a pale yellow solid (1.6 g, yield: 80%).

¹H NMR (400 MHz, DMSO-d₆): 7.67-7.70 (d, 4H), 7.46-7.53 (m, 14H),7.21-7.31 (m, 4H), 7.17-7.18 (d, 2H), 7.06-7.11 (m, 8H), 6.91-7.01 (m,22H), 3.75 (s, 12H), 1.35 (s, 12H).

(E) Further Compounds of the Formula I for Use in Accordance with theInvention

The compounds listed below were obtained analogously to the synthesesdescribed above:

(E1) Synthesis example 4 Compound ID320

¹H NMR (300 MHz, THF-d₈): δ 7.43-7.46 (d, 4H), 7.18-7.23 (t, 4H),7.00-7.08 (m, 16H), 6.81-6.96 (m, 18H), 3.74 (s, 12H)

(E2) Synthesis Example 5 Compound ID321

¹H NMR (300 MHz, THF-d₈): δ 7.37-7.50 (t, 8H), 7.37-7.40 (d, 4H),7.21-7.26 (d, 4H), 6.96-7.12 (m, 22H), 6.90-6.93 (d, 4H), 6.81-6.84 (d,8H), 3.74 (s, 12H)

(E3) Synthesis Example 6 Compound ID366

¹H NMR (400 MHz, DMSO-d6): δ 7.60-7.70 (t, 4H), 7.40-7.55 (d, 2H),7.17-7.29 (m, 8H), 7.07-7.09 (t, 4H), 7.06 (s, 2H), 6.86-7.00 (m, 24H),3.73 (s, 6H), 1.31 (s, 12H)

(E4) Synthesis Example 7 Compound ID368

¹H NMR (400 MHz, DMSO-d6): δ 7.48-7.55 (m, 8H), 7.42-7.46 (d, 4H),7.33-7.28 (d, 4H), 6.98-7.06 (m, 20H), 6.88-6.94 (m, 8H), 6.78-6.84 (d,4H), 3.73 (s, 12H), 1.27 (s, 18H)

(E5) Synthesis Example 8 Compound ID369

¹H NMR (400 MHz, THF-d8): δ 7.60-7.70 (t, 4H), 7.57-7.54 (d, 4H),7.48-7.51 (d, 4H), 7.39-7.44 (t, 6H), 7.32-7.33 (d, 2H), 7.14-7.27 (m,12H), 7.00-7.10 (m, 10H), 6.90-6.96 (m, 4H), 6.80-6.87 (m, 8H), 3.75 (s,12H), 1.42 (s, 12H)

(E6) Synthesis Example 9 Compound ID446

¹H NMR (400 MHz, dmso-d₆): δ 7.39-7.44 (m, 8H), 7.00-7.07 (m, 13H),6.89-6.94 (m, 19H), 6.79-6.81 (d, 4H), 3.73 (s, 18H)

(E7) Synthesis Example 10 Compound ID450

¹H NMR (400 MHz, dmso-d₆): δ 7.55-7.57 (d, 2H), 7.39-7.45 (m, 8H),6.99-7.04 (m, 15H), 6.85-6.93 (m, 19H), 6.78-6.80 (d, 4H), 3.72 (s,18H), 1.68-1.71 (m, 6H), 1.07 (m, 6H), 0.98-0.99 (m, 8H), 0.58 (m, 6H)

(E8) Synthesis Example 11 Compound ID452

¹H NMR (400 MHz, DMSO-d6): δ 7.38-7.44 (m, 8H), 7.16-7.19 (d, 4H),6.99-7.03 (m, 12H), 6.85-6.92 (m, 20H), 6.77-6.79 (d, 4H), 3.74 (s,18H), 2.00-2.25 (m, 4H), 1.25-1.50 (m, 6H)

(E9) Synthesis Example 12 Compound ID480

¹H NMR (400 MHz, DMSO-d6): δ 7.40-7.42 (d, 4H), 7.02-7.05 (d, 4H),6.96-6.99 (m, 28H), 6.74-6.77 (d, 4H), 3.73 (s, 6H), 3.71 (s, 12H)

(E10) Synthesis example 13 Compound ID518

¹H NMR (400 MHz, DMSO-d6): 7.46-7.51 (m, 8H), 7.10-7.12 (d, 2H),7.05-7.08 (d, 4H), 6.97-7.00 (d, 8H), 6.86-6.95 (m, 20H), 6.69-6.72 (m,2H), 3.74 (s, 6H), 3.72 (s, 12H), 1.24 (t, 12H)

(E11) Synthesis Example 14 Compound ID519

¹H NMR (400 MHz, DMSO-d6): 7.44-7.53 (m, 12H), 6.84-7.11 (m, 32H),6.74-6.77 (d, 2H), 3.76 (s, 6H), 3.74 (s, 6H), 2.17 (s, 6H), 2.13 (s,6H)

(E12) Synthesis Example 15 Compound ID521

¹H NMR (400 MHz, THF-d₆): 7.36-7.42 (m, 12H), 6.99-7.07 (m, 20H),6.90-6.92 (d, 4H), 6.81-6.84 (m, 8H), 6.66-6.69 (d, 4H), 3.74 (s, 12H),3.36-3.38 (q, 8H), 1.41-1.17 (t, 12H)

(E13) Synthesis Example 16 Compound ID522

¹H NMR (400 MHz, DMSO-d₆): 7.65 (s, 2H), 7.52-7.56 (t, 2H), 7.44-7.47(t, 1H), 7.37-7.39 (d, 2H), 7.20-7.22 (m, 10H), 7.05-7.08 (dd, 2H),6.86-6.94 (m, 8H), 6.79-6.80-6.86 (m, 12H), 6.68-6.73, (dd, 8H),6.60-6.62 (d, 4H), 3.68 (s, 12H), 3.62 (s, 6H)

(E14) Synthesis Example 17 Compound ID523

¹H NMR (400 MHz, THF-d₈): 7.54-7.56 (d, 2H), 7.35-7.40 (dd, 8H), 7.18(s, 2H), 7.00-7.08 (m, 18H), 6.90-6.92 (d, 4H), 6.81-6.86 (m, 12H), 3.75(s, 6H), 3.74 (s, 12H), 3.69 (s, 2H)

(E15) Synthesis Example 18 Compound ID565

¹H NMR (400 MHz, THF-d8): 7.97-8.00 (d, 2H), 7.86-7.89 (d, 2H),7.73-7.76 (d, 2H), 7.28-7.47 (m, 20H), 7.03-7.08 (m, 16H), 6.78-6.90 (m,12H), 3.93-3.99 (q, 4H), 3.77 (s, 6H), 1.32-1.36 (s, 6H)

(E16) Synthesis Example 19 Compound ID568

¹H NMR (400 MHz, DMSO-d6): 7.41-7.51 (m, 12H), 6.78-7.06 (m, 36H),3.82-3.84 (d, 4H), 3.79 (s, 12H), 1.60-1.80 (m, 2H), 0.60-1.60 (m, 28H)

(E17) Synthesis Example 20 Compound ID569

¹H NMR (400 MHz, DMSO-d6): 7.40-7.70 (m, 10H), 6.80-7.20 (m, 36H),3.92-3.93 (d, 4H), 2.81 (s, 12H), 0.60-1.90 (m, 56H)

(E18) Synthesis Example 21 Compound ID572

¹H NMR (400 MHz, THF-d8): 7.39-7.47 (m, 12H), 7.03-7.11 (m, 20H),6.39-6.99 (m, 8H), 6.83-6.90 (m, 8H), 3.78 (s, 6H), 3.76 (s, 6H), 2.27(s, 6H)

(E19) Synthesis Example 22 Compound ID573

¹H NMR (400 MHz, THF-d8): 7.43-7.51 (m, 20H), 7.05-7.12 (m, 24H),6.87-6.95 (m, 12H), 3.79 (s, 6H), 3.78 (s, 12H)

(E20) Synthesis Example 23 Compound ID575

¹H NMR (400 MHz, DMSO-d6): 7.35-7.55 (m, 8H), 7.15-7.45 (m, 4H),6.85-7.10 (m, 26H), 6.75-6.85 (d, 4H), 6.50-6.60 (d, 2H), 3.76 (s, 6H),3.74 (s, 12H)

(E21) Synthesis Example 24 Compound ID629

¹H NMR (400 MHz, THF-d₈): 7.50-7.56 (dd, 8H), 7.38-7.41 (dd, 4H),7.12-7.16 (d, 8H), 7.02-7.04 (dd, 8H), 6.91-6.93 (d, 4H), 6.82-6.84 (dd,8H), 6.65-6.68 (d, 4H) 3.87 (s, 6H), 3.74 (s, 12H)

(E22) Synthesis Example 25 Compound ID631

¹H NMR (400 MHz, THF-d₆): 7.52 (d, 2H), 7.43-7.47 (dd, 2H), 7.34-7.38(m, 8H), 7.12-7.14 (d, 2H), 6.99-7.03 (m, 12H), 6.81-6.92 (m, 20H), 3.74(s, 18H), 2.10 (s, 6H)

(F) Synthesis of Compounds of the Formula IV

(a) Coupling of p-anisidine and 2-bromo-9,9-dimethyl-9H-fluorene

To 0.24 ml (0.08 mmol) of P(t-Bu)₃ (d=0.68 g/ml) and 0.1 g of Pd₂(dba)₂[=(tris(dibenzylideneacetone)dipalladium(0)] (0.1 mmol) were added 10 mlto 15 ml of toluene (anhydrous, 99.8%), and the mixture was stirred atroom temperature for 10 min. 1.44 g (15 mmol) of sodium tert-butoxide(97.0%) were added and the mixture was stirred at room temperature for afurther 15 min. Subsequently, 2.73 g (11 mmol) of2-bromo-9,9-dimethyl-9H-fluorene were added and the reaction mixture wasstirred for a further 15 min. Finally, 1.23 g (10 mmol) of p-anisidinewere added and the mixture was stirred at 90° C. for 4 h.

The reaction mixture was admixed with water and the product wasprecipitated from hexane. The aqueous phase was additionally extractedwith ethyl acetate. The organic phase and the precipitated solid whichhad been filtered off were combined and purified by columnchromatography on an SiO₂ phase (10:1 hexane:ethyl acetate).

1.5 g (yield: 47.6%) of a yellow solid were obtained.

¹HNMR (300 MHz, C6D6): 6.7-7.6 (m, 11H), 5.00 (s, 1H,), 3.35 (s, 3H),1.37 (s, 6H)

(b) Coupling of the Product from (a) with tris(4-bromophenyl)amine

To 0.2 ml (0.07 mmol) of P(t-Bu)₃ (D=0.68 g/ml) and 0.02 g (0.1 mmol) ofpalladium acetate were added 25 ml of toluene (anhydrous), and themixture was stirred at room temperature for 10 min. 0.4 g (1.2 mmol) ofsodium tert-butoxide (97.0%) was added and the mixture was stirred atroom temperature for a further 15 min. Subsequently, 0.63 g (1.3 mmol)of tris(4-bromophenyl)amine was added and the reaction mixture wasstirred for a further 15 min. Finally, 1.3 g (1.4 mmol) of the productfrom step (a) were added and the mixture was stirred at 90° C. for 5 h.

The reaction mixture was admixed with ice-cold water and extracted withethyl acetate. The product was precipitated from a mixture ofhexane/ethyl acetate and purified by column chromatography on SiO₂ phase(9:1->5:1 hexane:ethyl acetate gradient).

0.7 g (yield: 45%) of a yellow product was obtained.

¹HNMR (300 MHz, C6D6): 6.6-7.6 (m, 45H), 3.28 (s, 9H), 1.26 (s, 18H)

(G) Synthesis of Compounds ID504

The preparation proceeded from(4-bromophenyl)bis(9,9-dimethyl-9H-fluoren-2-yl) (see ChemicalCommunications, 2004, 68-69), which was first reacted with4,4,5,5,4′,4′,5′,5′-octamethyl-[2,2′]bi[[1,3,2]dioxaborolanyl] (step a).This was followed by coupling with 9Br-DIPP-PDCI (step b). This wasfollowed by hydrolysis to give the anhydride (step c) and subsequentreaction with glycine to give the final compound (step d).

Step a:

A mixture of 30 g (54 mmol) of(4-bromophenyl)bis(9,9-dimethyl-9H-fluoren-2-yl), 41 g (162 mmol) of4,4,5,5,4′,4′,5′,5′-octamethyl-[2,2′]bi[[1,3,2]dioxaborolanyl], 1 g (1.4mmol) of Pd(dpf)₂Cl₂, 15.9 g (162 mmol) of potassium acetate and 300 mlof dioxane was heated to 80° C. and stirred for 36 h.

After cooling, the solvent was removed and the residue was dried at 50°C. in a vacuum drying cabinet.

Purification was effected by filtration through silica gel with theeluent 1:1 n-hexane:dichloromethane. After the removal of the reactant,the eluent was switched to dichloromethane. The product was isolated asa reddish and tacky residue. This was extracted by stirring withmethanol at RT for 0.5 h. The light-colored precipitate was filteredoff. After drying at 45° C. in a vacuum drying cabinet, 24 g of alight-colored solid were obtained, which corresponds to a yield of 74%.

Analytic Data

¹H NMR (500 MHz, CD₂Cl₂, 25° C.): δ=7.66-7.61 (m, 6H); 7.41-7.4 (m, 2H);7.33-7.25 (m, 6H); 7.13-7.12 (m, 2H); 7.09-7.07 (m, 2H); 1.40 (s, 12H);1.32 (s, 12H)

Step b:

17.8 g (32 mmol) of 9Br-DIPP-PDCI and 19 ml (95 mmol) of 5 molar NaOHwere introduced into 500 ml of dioxane. This mixture was degassed withargon for 30 min. Then 570 mg (1.1 mmol) of Pd[P(tBu)₃]₂ and 23 g (38mmol) of stage a were added and the mixture was stirred at 85° C. underargon for 17 h.

Purification was effected by column chromatography with the eluent 4:1dichloromethane:toluene.

22.4 g of a violet solid were obtained, which corresponds to a yield of74%.

Analytical Data:

¹H NMR (500 MHz, CH₂Cl₂, 25° C.): δ=8.59-8.56 (m, 2H); 8.46-8.38 (m,4H); 8.21-8.19 (d, 1H); 7.69-7.60 (m, 6H); 7.52-7.25 (m, 17H); 2.79-2.77(m, 2H); 1.44 (s, 12H); 1.17-1.15 (d, 12H)

Step c:

22.4 g (23 mmol) of step b and 73 g (1.3 mol) of KOH were introducedinto 200 ml of 2-methyl-2-butanol and the mixture was stirred at refluxfor 17 h.

After cooling, the reaction mixture was added to 1 l of ice-water+50 mlof concentrated acetic acid. The orange-brown solid was filtered througha frit and washed with water.

The solid was dissolved in dichloromethane and extracted withdemineralized water. 10 ml of concentrated acetic acid were added to theorganic phase, which was stirred at RT. The solvent was removed from thesolution. The residue was extracted by stirring with methanol at RT for30 min, filtered with suction through a frit and dried at 55° C. in avacuum drying cabinet.

This afforded 17.5 g of a violet solid, which corresponds to a yield of94%. The product was used unpurified in the next step.

Step d:

17.5 g (22 mmol) of stage c, 16.4 g (220 mmol) of glycine and 4 g (22mmol) of zinc acetate were introduced into 350 ml of N-methylpyrrolidoneand the mixture was stirred at 130° C. for 12 h.

After cooling, the reaction mixture was added to 1 l of demineralizedwater. The precipitate was filtered through a frit, washed with waterand dried at 70° C. in a vacuum drying cabinet.

Purification was effected by means of column chromatography with theeluent 3:1 dichloromethane:ethanol+2% triethylamine. The isolatedproduct was extracted by stirring at 60° C. with 50% acetic acid. Thesolid was filtered off with suction through a frit, washed with waterand dried at 80° C. in a vacuum drying cabinet.

7.9 g of a violet solid were obtained, which corresponds to a yield of42%.

Analytical Data:

¹H NMR (500 MHz, THF, 25° C.): δ=8.37-8.34 (m, 2H); 8.25-8.18 (m, 4H);8.12-8.10 (d, 1H); 7.74-7.70 (m, 4H); 7.59-7.53 (m, 4H); 7.45-7.43 (m,4H); 7.39-7.37 (m, 2H); 7.32-7.22 (m, 6H); 4.82 (s, 2H); 1.46 (s, 12H)

(H) Synthesis of Compounds ID662

ID662 was prepared by reacting the corresponding commercially availablehydroxamic acid [2-(4-butoxyphenyl)-N-hydroxyacetamide] with sodiumhydroxide.

LIST OF REFERENCE NUMERALS

-   110 Photovoltaic element-   112 Dye solar cell-   114 Substrate-   116 First electrode-   118 Blocking layer-   120 n-semiconductive material-   122 Dye-   124 Carrier element-   126 p-semiconductor-   128 Matrix material-   130 Silver in oxidized form-   132 Second electrode-   134 Layer structure-   136 Encapsulation-   138 Fermi level-   140 HOMO-   142 LUMO-   144 Characteristic for comparative sample without silver in oxidized    form, t=0-   146 Characteristic for comparative sample without silver in oxidized    form, t=2 days-   148 Characteristic for example 1 sample, t=0-   150 Characteristic for example 1 sample, t=2 days

1. A photovoltaic element for conversion of electromagnetic radiation toelectrical energy, especially dye solar cell, wherein the photovoltaicelement comprises at least one first electrode, at least onen-semiconductive metal oxide, at least one electromagneticradiation-absorbing dye, at least one solid organic p-semiconductor andat least one second electrode, wherein the p-semiconductor comprisessilver in oxidized form.
 2. The photovoltaic element according to claim1, wherein the p-semiconductor is producible or has been produced byapplying at least one p-conductive organic material and silver inoxidized form to at least one carrier element, wherein the silver ispreferably applied in the form of at least one silver(I) salt[Ag⁺]_(m)[A^(m−)] where A^(m−) is the anion of an organic or inorganicacid and m is an integer in the range from 1 to 3, preferably where mis
 1. 3. The photovoltaic element according to claim 2, wherein silveris applied in the form of at least one silver(I) salt [Ag⁺]_(m)[A^(m−)]where [A^(m−)] is an anion of an organic acid, preferably where theorganic acid has at least one fluorine group —F or cyano group.
 4. Thephotovoltaic element according to claim 3, wherein [A^(m−)] has astructure of the formula (II)

where R^(a) is a fluorine group —F or an alkyl radical, cycloalkylradical, aryl radical or heteroaryl radical each substituted by at leastone fluorine group or cyano group, and where X is —O⁻ or —N⁻—R^(b), andwhere R^(b) comprises a fluorine group —F or a cyano group, and whereR^(b) further comprises a group of the formula —S(O)₂ ⁻.
 5. Thephotovoltaic element according to claim 4, wherein R^(a) is selectedfrom the group consisting of —F, —CF₃, —CF₂—CF₃ and —CH₂—CN.
 6. Thephotovoltaic element according to claim 4 or 5, where X is —N⁻—R^(b),and where R^(b) is selected from the group consisting of —S(O)₂—F,—S(O)₂—CF₃, —S(O)₂—CF₂—CF₃ and —S(O)₂—CH₂—CN.
 7. The photovoltaicelement according to claim 3, wherein [A^(m−)] is selected from thegroup consisting of bis(trifluoromethylsulfonyl)imide (TFSI⁻),bis(trifluoroethylsulfonyl)imide, bis(fluorosulfonyl)imide andtrifluoromethylsulfonate, preferably where [A^(m−)] isbis(trifluoromethylsulfonyl)imide (TFSI⁻).
 8. The photovoltaic elementaccording to claim 3, wherein [A^(m−)] is a trifluoroacetate group. 9.The photovoltaic element according to claim 3, wherein [A^(m−)] is NO₃⁻.
 10. The photovoltaic element according to claim 3, wherein thep-semiconductor is producible or has been produced by applying at leastone p-conductive organic material and at least one silver(I) salt[Ag⁺]_(m)[A^(m−)] to at least one carrier element, the application beingeffected by deposition from a liquid phase comprising the at least onep-conductive organic material and the at least one silver(I) salt[Ag⁺]_(m)[A^(m−)].
 11. The photovoltaic element according to claim 10,wherein the liquid phase further comprises at least one solvent,especially an organic solvent, especially a solvent selected from:cyclohexanone; chlorobenzene; benzofuran; cyclopentanone.
 12. Thephotovoltaic element according to claim 11, wherein Ag⁺ and preferablyalso the anionic compound [A^(m−)] is in essentially homogeneousdistribution in the matrix material.
 13. The photovoltaic elementaccording to claim 11, wherein the matrix material comprises at leastone low molecular weight organic p-semiconductor.
 14. The photovoltaicelement according to claim 2, wherein the p-conductive organic materialcomprises a spiro compound, especially spiro-MeOTAD, and/or a compoundwith the structural formula:

in which A¹, A², A³ are each independently optionally substituted arylgroups or heteroaryl groups, R₁, R₂, R₃ are each independently selectedfrom the group consisting of the substituents —R, —OR, —NR₂, -A⁴-OR and-A⁴-NR₂, where R is selected from the group consisting of alkyl, aryland heteroaryl, and where A⁴ is an aryl group or heteroaryl group, andwhere n at each instance in formula I is independently a value of 0, 1,2 or 3, with the proviso that the sum of the individual n values is atleast 2 and at least two of the R¹, R² and R³ radicals are —OR and/or—NR₂.
 15. The photovoltaic element according to claim 1, furthercomprising at least one encapsulation, wherein the encapsulation isdesigned to shield the photovoltaic element, especially the electrodesand/or the p-semiconductor, from a surrounding atmosphere.
 16. Thephotovoltaic element according to claim 10, wherein the liquid phasecomprises the at least one silver(I) salt [Ag⁺]_(m)[A^(m−)] in aconcentration of 0.5 mM/ml to 50 mM/ml, more preferably in aconcentration of 1 mM/ml up to 20 mM/ml.
 17. A process for producing asolid organic p-semiconductor for use in an organic component,especially a photovoltaic element according to any of the precedingclaims, wherein at least one p-conductive organic matrix material and atleast silver in oxidized form, preferably at least one silver(I) salt[Ag⁺]_(m)[A^(m−)], are applied to at least one carrier element from atleast one liquid phase, where [A]⁻ is the anion of an organic orinorganic acid, and where the compound [Ag⁺]_(m)[A^(m−)] is preferablyAgNO₃ or silver bis(trifluoromethylsulfonyl)imide.
 18. The processaccording to claim 17, wherein the liquid phase further comprises atleast one solvent, especially an organic solvent, especially a solventselected from: cyclohexanone; chlorobenzene; benzofuran; cyclopentanone.19. The process according to claim 17, wherein the process is performedat least partly in a low-oxygen atmosphere.
 20. A process for producinga photovoltaic element, especially according to any of the precedingclaims relating to a photovoltaic element, wherein, in the process, atleast one first electrode, at least one n-semiconductive metal oxide, atleast one electromagnetic radiation-absorbing dye, at least one solidorganic p-semiconductor and at least one second electrode are provided,wherein the p-semiconductor is produced by a process according to claim17.